diff --git a/CLAUDE.md b/CLAUDE.md
index 1c6c1772..01de093a 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -42,8 +42,10 @@ src/
   gramps-js.js             # Entry point (registers the custom element)
   api.js                   # All API calls, auth helpers, localStorage utilities
   appState.js              # App-wide state initialisation
+  color.js                 # Gramps internal hex format converters (tag colours etc.)
   config.js                # Runtime config (window.grampsjsConfig); see below
   strings.js               # i18n string keys and language list
+  theme.js                 # Colour theme: applyScheme(), applyColors(), DEFAULT_PRIMARY/SECONDARY
   util.js                  # Shared helpers
   components/              # Reusable components
   views/                   # Page-level components
@@ -80,7 +82,7 @@ html`<grampsjs-icon path="${mdiInformation}"></grampsjs-icon>`
 
 Optional attributes: `color`, `height`, `width`, `rotate`.
 
-For action icon color (add/edit/delete buttons), use `color="var(--mdc-theme-secondary)"` — this is `#0277bd` and is consistent across light and dark mode.
+For action icon color (add/edit/delete buttons), use `color="var(--mdc-theme-secondary)"` — this is derived from the active secondary seed colour and adapts to light/dark mode.
 
 ### Mixins
 
diff --git a/global.css b/global.css
index 862c0b76..b4390874 100644
--- a/global.css
+++ b/global.css
@@ -11,8 +11,7 @@ body {
   /* Web Awesome color token overrides.
      default.css (loaded in index.html) defines --wa-* tokens inside @layer wa-theme,
      so these unlayered declarations win without !important. The --md-sys-color-*
-     values on the right are defined in the light/dark blocks below, so the
-     color picker automatically adapts to the active theme. */
+     values on the right are set dynamically by applyColors() in theme.js. */
   --wa-color-surface-raised: var(--md-sys-color-surface-container-high);
   --wa-color-surface-default: var(--md-sys-color-surface);
   --wa-color-surface-border: var(--md-sys-color-outline-variant);
@@ -29,7 +28,7 @@ body {
   --color-other: #ce93d8;
   --mdc-theme-primary: var(--md-sys-color-primary);
   --mdc-theme-on-primary: var(--md-sys-color-on-primary);
-  --mdc-theme-secondary: #0277bd;
+  --mdc-theme-secondary: var(--md-sys-color-secondary);
   --mdc-theme-on-secondary: rgba(255, 255, 255, 0.95);
   --mdc-theme-background: var(--md-sys-color-background);
   --mdc-theme-surface: var(--md-sys-color-surface);
@@ -49,11 +48,27 @@ body {
   --grampsjs-lightbox-font-color: #fff;
   --grampsjs-lightbox-nav-color: #aaa;
   --grampsjs-lightbox-nav-hover-color: #fff;
-  --grampsjs-alert-background-color: rgba(109, 76, 65, 0.15);
-  --grampsjs-alert-border-color: rgba(109, 76, 65, 0.7);
-  --grampsjs-alert-error-background-color: rgba(191, 54, 12, 0.2);
-  --grampsjs-alert-error-border-color: rgba(191, 54, 12, 0.7);
-  --grampsjs-alert-error-font-color: #bf360c;
+  --grampsjs-alert-background-color: color-mix(
+    in srgb,
+    var(--md-sys-color-primary) 15%,
+    transparent
+  );
+  --grampsjs-alert-border-color: color-mix(
+    in srgb,
+    var(--md-sys-color-primary) 70%,
+    transparent
+  );
+  --grampsjs-alert-error-background-color: color-mix(
+    in srgb,
+    var(--md-sys-color-error) 20%,
+    transparent
+  );
+  --grampsjs-alert-error-border-color: color-mix(
+    in srgb,
+    var(--md-sys-color-error) 70%,
+    transparent
+  );
+  --grampsjs-alert-error-font-color: var(--md-sys-color-error);
   --grampsjs-map-marker-color: #ea4335;
   --grampsjs-map-filter-badge-color: #ba1b1b;
   --grampsjs-logout-font-color: #c62828;
@@ -64,16 +79,59 @@ body {
   --grampsjs-task-open: #007bff;
   --grampsjs-task-progress: #ff9800;
   --grampsjs-task-done: rgba(65, 173, 73, 0.4);
-  --grampsjs-editable-title-hover-background-color: rgba(2, 119, 189, 0.2);
-  --grampsjs-delete-all-filter-chip-color: rgba(109, 76, 65, 0.32);
-  --grampsjs-connection-chart-border-color: rgba(137, 107, 94, 0.4);
+  --grampsjs-editable-title-hover-background-color: color-mix(
+    in srgb,
+    var(--mdc-theme-secondary) 20%,
+    transparent
+  );
+  --grampsjs-delete-all-filter-chip-color: color-mix(
+    in srgb,
+    var(--md-sys-color-primary) 32%,
+    transparent
+  );
+  --grampsjs-connection-chart-border-color: color-mix(
+    in srgb,
+    var(--md-sys-color-primary) 40%,
+    transparent
+  );
   --grampsjs-connection-chart-person-box: #e6e6e6;
-  --grampsjs-editable-list-hover-background-color: rgba(2, 119, 189, 0.1);
-  --grampsjs-editable-list-active-background-color: rgba(2, 119, 189, 0.2);
-  --grampsjs-editable-list-selected-active-background-color: rgba(2, 119, 189, 0.3);
-  --grampsjs-editable-list-selected-hover-background-color: rgba(2, 119, 189, 0.4);
-  --grampsjs-editable-list-selected-background-color: rgba(2, 119, 189, 0.5);
-  --grampsjs-mobile-table-sort-menu-color: rgba(109, 76, 65, 0.3);
+  --grampsjs-editable-list-hover-background-color: color-mix(
+    in srgb,
+    var(--mdc-theme-secondary) 10%,
+    transparent
+  );
+  --grampsjs-editable-list-active-background-color: color-mix(
+    in srgb,
+    var(--mdc-theme-secondary) 20%,
+    transparent
+  );
+  --grampsjs-editable-list-selected-active-background-color: color-mix(
+    in srgb,
+    var(--mdc-theme-secondary) 30%,
+    transparent
+  );
+  --grampsjs-editable-list-selected-hover-background-color: color-mix(
+    in srgb,
+    var(--mdc-theme-secondary) 40%,
+    transparent
+  );
+  --grampsjs-editable-list-selected-background-color: color-mix(
+    in srgb,
+    var(--mdc-theme-secondary) 50%,
+    transparent
+  );
+  --grampsjs-mobile-table-sort-menu-color: color-mix(
+    in srgb,
+    var(--md-sys-color-primary) 30%,
+    transparent
+  );
+  --grampsjs-color-link-font: var(--mdc-theme-secondary);
+  --grampsjs-color-link-hover: color-mix(
+    in srgb,
+    var(--mdc-theme-secondary) 80%,
+    black
+  );
+  --grampsjs-color-page-loading-progress: var(--mdc-theme-secondary);
 }
 
 :root[data-theme='light'] {
@@ -116,9 +174,6 @@ body {
   --grampsjs-color-skeleton-background: #eee;
   --grampsjs-color-skeleton-base: #ececec;
   --grampsjs-color-skeleton-shine: #f5f5f5;
-  --grampsjs-color-link-font: #0d47a1;
-  --grampsjs-color-link-hover: #1976d2;
-  --grampsjs-color-page-loading-progress: #4fc3f7;
   --grampsjs-color-revision-deleted-background-red: #ffebe9;
   --grampsjs-color-revision-added-background-green: #dafbe1;
   --grampsjs-color-revision-moved-background-blue: #ddf4ff;
@@ -131,55 +186,7 @@ body {
   --grampsjs-color-ytree-expand-font: #555;
   --grampsjs-color-ytree-default-person-icon-background: #bbb;
   --grampsjs-note-color: #333;
-  --md-sys-color-primary: rgb(109, 76, 65);
-  --md-sys-color-surface-tint: rgb(109, 76, 65);
-  --md-sys-color-on-primary: rgb(255, 255, 255);
-  --md-sys-color-primary-container: rgb(255, 219, 207);
-  --md-sys-color-on-primary-container: rgb(57, 12, 0);
-  --md-sys-color-secondary: rgb(49, 98, 141);
-  --md-sys-color-on-secondary: rgb(255, 255, 255);
-  --md-sys-color-secondary-container: rgb(207, 229, 255);
-  --md-sys-color-on-secondary-container: rgb(0, 29, 52);
-  --md-sys-color-tertiary: rgb(106, 94, 47);
-  --md-sys-color-on-tertiary: rgb(255, 255, 255);
-  --md-sys-color-tertiary-container: rgb(243, 226, 167);
-  --md-sys-color-on-tertiary-container: rgb(34, 27, 0);
-  --md-sys-color-error: rgb(186, 26, 26);
-  --md-sys-color-on-error: rgb(255, 255, 255);
-  --md-sys-color-error-container: rgb(255, 218, 214);
-  --md-sys-color-on-error-container: rgb(65, 0, 2);
-  --md-sys-color-background: #fff;;
-  --md-sys-color-on-background: var(--grampsjs-body-font-color);
-  --md-sys-color-surface: #fff;
-  --md-sys-color-on-surface: var(--grampsjs-body-font-color);
-  --md-sys-color-surface-variant: rgb(232, 224, 222);
-  --md-sys-color-on-surface-variant: rgb(83, 67, 63);
-  --md-sys-color-outline: rgb(133, 115, 110);
-  --md-sys-color-outline-variant: rgb(200, 200, 200);
-  --md-sys-color-shadow: rgb(0, 0, 0);
-  --md-sys-color-scrim: rgb(0, 0, 0);
-  --md-sys-color-inverse-surface: rgb(57, 46, 43);
-  --md-sys-color-inverse-on-surface: rgb(255, 237, 232);
-  --md-sys-color-inverse-primary: rgb(255, 181, 156);
-  --md-sys-color-primary-fixed: rgb(255, 219, 207);
-  --md-sys-color-on-primary-fixed: rgb(57, 12, 0);
-  --md-sys-color-primary-fixed-dim: rgb(255, 181, 156);
-  --md-sys-color-on-primary-fixed-variant: rgb(114, 53, 32);
-  --md-sys-color-secondary-fixed: rgb(207, 229, 255);
-  --md-sys-color-on-secondary-fixed: rgb(0, 29, 52);
-  --md-sys-color-secondary-fixed-dim: rgb(157, 203, 251);
-  --md-sys-color-on-secondary-fixed-variant: rgb(18, 74, 115);
-  --md-sys-color-tertiary-fixed: rgb(243, 226, 167);
-  --md-sys-color-on-tertiary-fixed: rgb(34, 27, 0);
-  --md-sys-color-tertiary-fixed-dim: rgb(214, 198, 141);
-  --md-sys-color-on-tertiary-fixed-variant: rgb(81, 70, 26);
-  --md-sys-color-surface-dim: rgb(232, 214, 209);
-  --md-sys-color-surface-bright: rgb(255, 248, 246);
-  --md-sys-color-surface-container-lowest: rgb(245, 245, 245);
-  --md-sys-color-surface-container-low: rgb(240, 240, 240);
-  --md-sys-color-surface-container: #fff;
-  --md-sys-color-surface-container-high: #fff;
-  --md-sys-color-surface-container-highest: whitesmoke;
+  /* --md-sys-color-* tokens are set dynamically by applyColors() in theme.js */
 }
 
 :root[data-theme='dark'] {
@@ -222,9 +229,6 @@ body {
   --grampsjs-color-skeleton-background: #222;
   --grampsjs-color-skeleton-base: #232323;
   --grampsjs-color-skeleton-shine: #1a1a1a;
-  --grampsjs-color-link-font: #5193f6;
-  --grampsjs-color-link-hover: #62adf8;
-  --grampsjs-color-page-loading-progress: #42a6d2;
   --grampsjs-color-revision-deleted-background-red: rgba(248, 81, 73, 0.3);
   --grampsjs-color-revision-added-background-green: rgba(46, 160, 67, 0.15);
   --grampsjs-color-revision-moved-background-blue: rgba(56, 139, 253, 0.1);
@@ -238,55 +242,7 @@ body {
   --grampsjs-color-ytree-default-person-icon-background: var(--md-sys-color-surface-container);
   --grampsjs-note-color: #ccc;
   --grampsjs-map-marker-color: #bb1f11;
-  --md-sys-color-primary: #8d7168;
-  --md-sys-color-surface-tint: rgb(233, 189, 174);
-  --md-sys-color-on-primary: rgba(0, 0, 0, 0.8);
-  --md-sys-color-primary-container: rgb(109, 76, 65);
-  --md-sys-color-on-primary-container: rgb(235, 190, 176);
-  --md-sys-color-secondary: rgb(156, 203, 251);
-  --md-sys-color-on-secondary: rgb(0, 51, 84);
-  --md-sys-color-secondary-container: rgb(49, 98, 141);
-  --md-sys-color-on-secondary-container: rgb(189, 220, 255);
-  --md-sys-color-tertiary: rgb(214, 198, 141);
-  --md-sys-color-on-tertiary: rgb(57, 48, 5);
-  --md-sys-color-tertiary-container: rgb(106, 94, 47);
-  --md-sys-color-on-tertiary-container: rgb(233, 216, 158);
-  --md-sys-color-error: rgb(255, 180, 171);
-  --md-sys-color-on-error: rgb(105, 0, 4);
-  --md-sys-color-error-container: rgb(186, 26, 26);
-  --md-sys-color-on-error-container: rgb(255, 205, 199);
-  --md-sys-color-background: rgb(22, 19, 18);
-  --md-sys-color-on-background: rgb(233, 225, 222);
-  --md-sys-color-surface: rgb(20, 19, 19);
-  --md-sys-color-on-surface: rgb(229, 226, 225);
-  --md-sys-color-surface-variant: rgb(68, 71, 72);
-  --md-sys-color-on-surface-variant: rgb(196, 199, 200);
-  --md-sys-color-outline: rgb(142, 145, 146);
-  --md-sys-color-outline-variant: rgb(68, 71, 72);
-  --md-sys-color-shadow: rgb(0, 0, 0);
-  --md-sys-color-scrim: rgb(0, 0, 0);
-  --md-sys-color-inverse-surface: rgb(229, 226, 225);
-  --md-sys-color-inverse-on-surface: rgb(49, 48, 48);
-  --md-sys-color-inverse-primary: rgb(121, 86, 75);
-  --md-sys-color-primary-fixed: rgb(255, 219, 207);
-  --md-sys-color-on-primary-fixed: rgb(45, 21, 13);
-  --md-sys-color-primary-fixed-dim: rgb(233, 189, 174);
-  --md-sys-color-on-primary-fixed-variant: rgb(94, 63, 53);
-  --md-sys-color-secondary-fixed: rgb(207, 229, 255);
-  --md-sys-color-on-secondary-fixed: rgb(0, 29, 51);
-  --md-sys-color-secondary-fixed-dim: rgb(156, 203, 251);
-  --md-sys-color-on-secondary-fixed-variant: rgb(17, 74, 115);
-  --md-sys-color-tertiary-fixed: rgb(243, 226, 167);
-  --md-sys-color-on-tertiary-fixed: rgb(34, 27, 0);
-  --md-sys-color-tertiary-fixed-dim: rgb(214, 198, 141);
-  --md-sys-color-on-tertiary-fixed-variant: rgb(81, 70, 26);
-  --md-sys-color-surface-dim: rgb(20, 19, 19);
-  --md-sys-color-surface-bright: rgb(58, 57, 57);
-  --md-sys-color-surface-container-lowest: rgb(14, 14, 14);
-  --md-sys-color-surface-container-low: rgb(28, 27, 27);
-  --md-sys-color-surface-container: rgb(32, 31, 31);
-  --md-sys-color-surface-container-high: rgb(42, 42, 42);
-  --md-sys-color-surface-container-highest: rgb(53, 52, 52);
+  /* --md-sys-color-* tokens are set dynamically by applyColors() in theme.js */
   --mdc-select-fill-color: var(--md-sys-color-surface-container-highest);
   --mdc-select-ink-color: var(--md-sys-color-on-surface);
   --mdc-select-label-ink-color: rgba(255, 255, 255, 0.5);
diff --git a/package-lock.json b/package-lock.json
index 7de948a7..d3680e77 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,6 +11,7 @@
       "dependencies": {
         "@awesome.me/webawesome": "^3.4.0",
         "@hpcc-js/wasm": "^2.22.4",
+        "@material/material-color-utilities": "^0.4.0",
         "@material/mwc-button": "^0.27.0",
         "@material/mwc-circular-progress": "^0.27.0",
         "@material/mwc-drawer": "^0.27.0",
@@ -2859,6 +2860,11 @@
         "tslib": "^2.1.0"
       }
     },
+    "node_modules/@material/material-color-utilities": {
+      "version": "0.4.0",
+      "resolved": "https://registry.npmjs.org/@material/material-color-utilities/-/material-color-utilities-0.4.0.tgz",
+      "integrity": "sha512-dlq6VExJReb8dhjj3a/yTigr3ncNwoFmL5Iy2ENtbDX03EmNeOEdZ+vsaGrj7RTuO+mB7L58II4LCsl4NpM8uw=="
+    },
     "node_modules/@material/menu": {
       "version": "14.0.0-canary.53b3cad2f.0",
       "resolved": "https://registry.npmjs.org/@material/menu/-/menu-14.0.0-canary.53b3cad2f.0.tgz",
@@ -16642,6 +16648,11 @@
         "tslib": "^2.1.0"
       }
     },
+    "@material/material-color-utilities": {
+      "version": "0.4.0",
+      "resolved": "https://registry.npmjs.org/@material/material-color-utilities/-/material-color-utilities-0.4.0.tgz",
+      "integrity": "sha512-dlq6VExJReb8dhjj3a/yTigr3ncNwoFmL5Iy2ENtbDX03EmNeOEdZ+vsaGrj7RTuO+mB7L58II4LCsl4NpM8uw=="
+    },
     "@material/menu": {
       "version": "14.0.0-canary.53b3cad2f.0",
       "resolved": "https://registry.npmjs.org/@material/menu/-/menu-14.0.0-canary.53b3cad2f.0.tgz",
diff --git a/package.json b/package.json
index ff286694..e866c236 100644
--- a/package.json
+++ b/package.json
@@ -127,6 +127,7 @@
   "dependencies": {
     "@awesome.me/webawesome": "^3.4.0",
     "@hpcc-js/wasm": "^2.22.4",
+    "@material/material-color-utilities": "^0.4.0",
     "@material/mwc-button": "^0.27.0",
     "@material/mwc-circular-progress": "^0.27.0",
     "@material/mwc-drawer": "^0.27.0",
@@ -163,4 +164,4 @@
     "pwa-helpers": "^0.9.1",
     "tippy.js": "^6.3.7"
   }
-}
\ No newline at end of file
+}
diff --git a/src/GrampsJs.js b/src/GrampsJs.js
index edaccd72..1168b5cf 100644
--- a/src/GrampsJs.js
+++ b/src/GrampsJs.js
@@ -39,7 +39,7 @@ import './components/GrampsjsUndoTransaction.js'
 import './components/GrampsjsUpdateAvailable.js'
 import './components/GrampsjsUpgradeDb.js'
 import {sharedStyles} from './SharedStyles.js'
-import {applyTheme} from './theme.js'
+import {applyScheme, DEFAULT_PRIMARY, DEFAULT_SECONDARY} from './theme.js'
 import {handleOIDCCallback, handleOIDCComplete} from './oidc.js'
 
 const LOADING_STATE_INITIAL = 0
@@ -661,10 +661,18 @@ export class GrampsJs extends LitElement {
       this._loadFrontendStrings(this.appState.settings.lang)
     }
 
-    applyTheme(this.appState.settings.theme)
+    applyScheme(
+      DEFAULT_PRIMARY,
+      DEFAULT_SECONDARY,
+      this.appState.settings.theme
+    )
     const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)')
     mediaQuery.addEventListener('change', () =>
-      applyTheme(this.appState.settings.theme)
+      applyScheme(
+        DEFAULT_PRIMARY,
+        DEFAULT_SECONDARY,
+        this.appState.settings.theme
+      )
     )
   }
 
diff --git a/src/theme.js b/src/theme.js
index f07a7885..65dddf28 100644
--- a/src/theme.js
+++ b/src/theme.js
@@ -1,3 +1,16 @@
+import {
+  DynamicScheme,
+  Hct,
+  MaterialDynamicColors,
+  TonalPalette,
+  Variant,
+  argbFromHex,
+  hexFromArgb,
+} from '@material/material-color-utilities'
+
+export const DEFAULT_PRIMARY = '#6d4c41'
+export const DEFAULT_SECONDARY = '#0277bd'
+
 export function getSystemTheme() {
   return window.matchMedia('(prefers-color-scheme: dark)').matches
     ? 'dark'
@@ -8,6 +21,100 @@ export function getCurrentTheme(theme) {
   return theme === undefined || theme === 'system' ? getSystemTheme() : theme
 }
 
-export function applyTheme(theme) {
-  document.documentElement.setAttribute('data-theme', getCurrentTheme(theme))
+function toKebabCase(str) {
+  return str.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase()
+}
+
+export function applyColors(
+  primaryHex = DEFAULT_PRIMARY,
+  secondaryHex = DEFAULT_SECONDARY,
+  isDark = false
+) {
+  const primaryHct = Hct.fromInt(argbFromHex(primaryHex))
+  const secondaryHct = Hct.fromInt(argbFromHex(secondaryHex))
+  const secondaryPalette = TonalPalette.fromHueAndChroma(
+    secondaryHct.hue,
+    secondaryHct.chroma
+  )
+
+  const primaryPalette = TonalPalette.fromHueAndChroma(
+    primaryHct.hue,
+    primaryHct.chroma
+  )
+
+  const scheme = new DynamicScheme({
+    sourceColorHct: primaryHct,
+    variant: Variant.TONAL_SPOT,
+    isDark,
+    contrastLevel: 0,
+    // Preserve the seed's own hue+chroma rather than TONAL_SPOT's fixed values.
+    primaryPalette,
+    secondaryPalette,
+    // Chroma 0 → pure neutral grays; no hue tint bleeds into surfaces.
+    neutralPalette: TonalPalette.fromHueAndChroma(primaryHct.hue, 0),
+    neutralVariantPalette: TonalPalette.fromHueAndChroma(primaryHct.hue, 0),
+  })
+
+  const root = document.documentElement
+  for (const [name, color] of Object.entries(MaterialDynamicColors)) {
+    if (typeof color?.getArgb !== 'function') continue
+    root.style.setProperty(
+      `--md-sys-color-${toKebabCase(name)}`,
+      hexFromArgb(color.getArgb(scheme))
+    )
+  }
+
+  // Primary: use seed's own tone clamped to [30, 50] so users see their chosen
+  // colour on the app bar. Tone 30-50 always reads white on-primary text.
+  const primaryTone = isDark
+    ? Math.min(80, Math.max(60, Math.round(primaryHct.tone)))
+    : Math.min(50, Math.max(30, Math.round(primaryHct.tone)))
+  root.style.setProperty(
+    '--md-sys-color-primary',
+    hexFromArgb(primaryPalette.tone(primaryTone))
+  )
+
+  // M3 achromatic tones 90-98 are darker than expected for a web app.
+  // Override light-mode surfaces to lighter neutrals.
+  if (!isDark) {
+    root.style.setProperty('--md-sys-color-background', '#ffffff')
+    root.style.setProperty('--md-sys-color-surface', '#ffffff')
+    // lowest/low/container → menus, cards, sheets: white
+    root.style.setProperty('--md-sys-color-surface-container-lowest', '#ffffff')
+    root.style.setProperty('--md-sys-color-surface-container-low', '#ffffff')
+    root.style.setProperty('--md-sys-color-surface-container', '#ffffff')
+    // high/highest → filled input and select backgrounds: light gray
+    root.style.setProperty(
+      '--md-sys-color-surface-container-high',
+      'rgb(240, 240, 240)'
+    )
+    root.style.setProperty(
+      '--md-sys-color-surface-container-highest',
+      'rgb(235, 235, 235)'
+    )
+  }
+
+  // Action color for edit/add/delete buttons: clamp tone to a readable range
+  // so very light or very dark seeds still contrast against their background.
+  const actionTone = isDark
+    ? Math.min(80, Math.max(60, Math.round(secondaryHct.tone)))
+    : Math.min(55, Math.max(30, Math.round(secondaryHct.tone)))
+  root.style.setProperty(
+    '--mdc-theme-secondary',
+    hexFromArgb(secondaryPalette.tone(actionTone))
+  )
+  root.style.setProperty(
+    '--mdc-theme-on-secondary',
+    actionTone < 60 ? 'rgba(255, 255, 255, 0.95)' : 'rgba(0, 0, 0, 0.87)'
+  )
+}
+
+export function applyScheme(
+  primaryHex = DEFAULT_PRIMARY,
+  secondaryHex = DEFAULT_SECONDARY,
+  theme
+) {
+  const isDark = getCurrentTheme(theme) === 'dark'
+  document.documentElement.setAttribute('data-theme', isDark ? 'dark' : 'light')
+  applyColors(primaryHex, secondaryHex, isDark)
 }
diff --git a/src/views/GrampsjsViewSettingsUser.js b/src/views/GrampsjsViewSettingsUser.js
index 8986ff83..3f66e0ca 100644
--- a/src/views/GrampsjsViewSettingsUser.js
+++ b/src/views/GrampsjsViewSettingsUser.js
@@ -18,7 +18,7 @@ import {GrampsjsView} from './GrampsjsView.js'
 import {mdiCheck, mdiContentCopy} from '@mdi/js'
 import {__APIHOST__} from '../api.js'
 import {fireEvent} from '../util.js'
-import {applyTheme} from '../theme.js'
+import {applyScheme, DEFAULT_PRIMARY, DEFAULT_SECONDARY} from '../theme.js'
 import {DEFAULT_TREE_VIEW, TREE_VIEWS} from '../treeDefaults.js'
 
 export class GrampsjsViewSettingsUser extends GrampsjsView {
@@ -186,7 +186,7 @@ export class GrampsjsViewSettingsUser extends GrampsjsView {
   _handleThemeSelected(event) {
     const theme = event.target.value
     this.appState.updateSettings({theme})
-    applyTheme(theme)
+    applyScheme(DEFAULT_PRIMARY, DEFAULT_SECONDARY, theme)
   }
 
   renderTreePreferences() {
diff --git a/vitest.config.js b/vitest.config.js
index af99b03d..342315f6 100644
--- a/vitest.config.js
+++ b/vitest.config.js
@@ -8,5 +8,12 @@ export default defineConfig({
       reporter: ['text', 'lcov'],
       include: ['src/**/*.js'],
     },
+    server: {
+      deps: {
+        // ESM imports in this package lack .js extensions, which Node.js
+        // strict ESM requires. Inline through Vite's bundler instead.
+        inline: ['@material/material-color-utilities'],
+      },
+    },
   },
 })