diff --git a/backend/main.py b/backend/main.py
index e1bf01d..262216e 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -383,6 +383,28 @@ def _migrate():
         except Exception:
             pass
 
+        # ── Theme inheritance ────────────────────────────────────────────
+        # These five colours used to carry a hardcoded column default, so every
+        # user row held a concrete value and the admin instance default could
+        # never apply. Clear the ones that still hold exactly that old default
+        # so they inherit again. A user who deliberately picked the same colour
+        # also inherits now — which is the same colour, until an admin changes
+        # the instance default.
+        for col, old_default in (("primary_color", "#4285f4"),
+                                 ("accent_color", "#ea4335"),
+                                 ("today_color", "#4285f4"),
+                                 ("month_divider_color", "#7090c0"),
+                                 ("month_label_color", "#7090c0")):
+            try:
+                conn.execute(text(
+                    f"UPDATE user_settings SET {col} = NULL "
+                    f"WHERE lower({col}) = lower(:old)"
+                ), {"old": old_default})
+                conn.commit()
+            except Exception:
+                pass
+
+
 _migrate()
 
 app = FastAPI(title="Calendarr", docs_url=None, redoc_url=None,
diff --git a/backend/models.py b/backend/models.py
index 0a42d9a..cdc77ce 100644
--- a/backend/models.py
+++ b/backend/models.py
@@ -95,16 +95,19 @@ class UserSettings(Base):
     user_id = Column(Integer, ForeignKey("users.id"), unique=True, nullable=False)
     default_view = Column(String(20), default="month")
     week_start_day = Column(String(10), default="monday")
-    primary_color = Column(String(7), default="#4285f4")
-    accent_color = Column(String(7), default="#ea4335")
-    today_color = Column(String(7), default="#4285f4")
+    # NULL = inherit the admin instance default (see admin_router). A baked-in
+    # column default would mean every user always *has* an own colour, so the
+    # instance default could never apply — which is exactly what happened.
+    primary_color = Column(String(7), nullable=True)
+    accent_color = Column(String(7), nullable=True)
+    today_color = Column(String(7), nullable=True)
     dim_past_events = Column(Boolean, default=False)
     text_contrast = Column(Integer, default=3)
     line_contrast = Column(Integer, default=3)
     hour_height = Column(Integer, default=60)
     language = Column(String(5), default="de")
-    month_divider_color = Column(String(7), default="#7090c0")
-    month_label_color = Column(String(7), default="#7090c0")
+    month_divider_color = Column(String(7), nullable=True)  # NULL = inherit
+    month_label_color = Column(String(7), nullable=True)    # NULL = inherit
     text_color = Column(String(7), nullable=True)   # Override für --text-1 (NULL = nutze text_contrast)
     line_color = Column(String(7), nullable=True)   # Override für --border  (NULL = nutze line_contrast)
     bg_color   = Column(String(7), nullable=True)   # Override für --bg-app  (NULL = Default)
diff --git a/backend/routers/settings_router.py b/backend/routers/settings_router.py
index 093ad43..d6472ca 100644
--- a/backend/routers/settings_router.py
+++ b/backend/routers/settings_router.py
@@ -108,8 +108,10 @@ def _settings_dict(s: models.UserSettings) -> dict:
         "line_contrast": s.line_contrast or 3,
         "hour_height": s.hour_height or 60,
         "language": s.language or "de",
-        "month_divider_color": s.month_divider_color or "#7090c0",
-        "month_label_color": s.month_label_color or "#7090c0",
+        # NULL stays NULL: the client resolves it against the admin instance
+        # default. Substituting a colour here would hide the inheritance.
+        "month_divider_color": s.month_divider_color,
+        "month_label_color": s.month_label_color,
         "text_color": s.text_color,
         "line_color": s.line_color,
         "bg_color":   s.bg_color,
@@ -186,7 +188,7 @@ def update_settings(
     # For these three override colours, an explicit null is meaningful
     # ("reset to default") and must be persisted as NULL. All other fields
     # keep the previous behaviour where a null/missing value is ignored.
-    NULLABLE_OVERRIDES = {"text_color", "line_color", "bg_color", "surface_color", "hover_highlight_color", "icon_inactive_color", "icon_active_color", "day_hover_color", "day_selected_color", "day_bg_color", "today_bg_color", "group_visible_calendar_id", "default_reminder_minutes", "default_event_duration_minutes", "share_calendar_icon"}
+    NULLABLE_OVERRIDES = {"text_color", "line_color", "bg_color", "surface_color", "hover_highlight_color", "icon_inactive_color", "icon_active_color", "day_hover_color", "day_selected_color", "day_bg_color", "today_bg_color", "group_visible_calendar_id", "default_reminder_minutes", "default_event_duration_minutes", "share_calendar_icon", "primary_color", "accent_color", "today_color", "month_divider_color", "month_label_color"}
     update_data = data.model_dump(exclude_unset=True)
 
     # Merge sync-flag overrides into the stored account-wide JSON map. Only known
diff --git a/backend/tests/test_theme_inheritance.py b/backend/tests/test_theme_inheritance.py
new file mode 100644
index 0000000..ed823e8
--- /dev/null
+++ b/backend/tests/test_theme_inheritance.py
@@ -0,0 +1,75 @@
+"""Theme colours: a user without an own colour must inherit the admin default.
+
+These five colours used to carry a hardcoded column default, which meant every
+user row always held a concrete value — so the admin's instance default could
+never apply to them, however it was configured.
+"""
+
+import models
+from conftest import auth, create_user, register_admin
+from database import SessionLocal
+
+INHERITABLE = ["primary_color", "accent_color", "today_color",
+               "month_divider_color", "month_label_color"]
+
+
+def db_session():
+    return SessionLocal()
+
+
+def test_new_user_has_no_own_colours(client):
+    """A fresh account inherits — nothing is baked into its row."""
+    admin_token = register_admin(client, "admin", "pw")
+    uid, token = create_user(client, admin_token, "hugo")
+
+    with db_session() as db:
+        s = db.query(models.UserSettings).filter(
+            models.UserSettings.user_id == uid).one()
+        for col in INHERITABLE:
+            assert getattr(s, col) is None, f"{col} should inherit, got {getattr(s, col)!r}"
+
+    body = client.get("/api/settings/", headers=auth(token)).json()
+    for col in INHERITABLE:
+        assert body[col] is None
+
+
+def test_setup_admin_also_inherits(client):
+    """The first-run admin is created on a different code path."""
+    token = register_admin(client, "admin", "pw")
+    body = client.get("/api/settings/", headers=auth(token)).json()
+    for col in INHERITABLE:
+        assert body[col] is None
+
+
+def test_choosing_a_colour_is_stored(client):
+    admin_token = register_admin(client, "admin", "pw")
+    _, token = create_user(client, admin_token, "hugo")
+
+    r = client.put("/api/settings/", headers=auth(token),
+                   json={"primary_color": "#58B900"})
+    assert r.status_code == 200, r.text
+    assert client.get("/api/settings/", headers=auth(token)).json()["primary_color"] == "#58B900"
+
+
+def test_reset_clears_back_to_inheriting(client):
+    """The reset button sends null, and null has to persist — otherwise
+    "reset" would just freeze today's admin default into the user's row."""
+    admin_token = register_admin(client, "admin", "pw")
+    _, token = create_user(client, admin_token, "hugo")
+
+    client.put("/api/settings/", headers=auth(token), json={"primary_color": "#58B900"})
+    r = client.put("/api/settings/", headers=auth(token), json={"primary_color": None})
+    assert r.status_code == 200, r.text
+    assert client.get("/api/settings/", headers=auth(token)).json()["primary_color"] is None
+
+
+def test_unrelated_save_does_not_invent_a_colour(client):
+    """Saving some other setting must not write a colour into the row."""
+    admin_token = register_admin(client, "admin", "pw")
+    _, token = create_user(client, admin_token, "hugo")
+
+    client.put("/api/settings/", headers=auth(token), json={"week_start_day": "sunday"})
+    body = client.get("/api/settings/", headers=auth(token)).json()
+    assert body["week_start_day"] == "sunday"
+    for col in INHERITABLE:
+        assert body[col] is None
diff --git a/frontend/js/calendar.js b/frontend/js/calendar.js
index ecfb2d9..7f21fc4 100644
--- a/frontend/js/calendar.js
+++ b/frontend/js/calendar.js
@@ -3761,8 +3761,13 @@ function settingRowHtml(def) {
     valueHtml = `<button type="button" class="sync-toggle ${val ? 'on' : ''}" data-vtoggle="${def.key}" role="switch" aria-checked="${!!val}"></button>`;
   } else if (def.type === 'color') {
     const hex = normalizeHex(val, baseColor(def.key));
+    // No own value means the row inherits the admin instance default. The
+    // field still shows that colour, but saving must send null — writing the
+    // hex back would freeze today's admin default into the user's row and
+    // later admin changes would stop reaching them.
+    const inherits = val == null ? ' data-inherit="1"' : '';
     valueHtml = `<div class="settings-color-ctl">
-      <input type="text" class="ev-color-hex" data-shex="${def.key}" maxlength="7" spellcheck="false" value="${hex}" />
+      <input type="text" class="ev-color-hex" data-shex="${def.key}" maxlength="7" spellcheck="false" value="${hex}"${inherits} />
       <div class="ev-color-preview" data-sprev="${def.key}" style="background:${hex}" title="${escHtml(t('color_pick'))}"></div>
       <button type="button" class="icon-btn ev-color-reset" data-sreset="${def.key}" title="${escHtml(t('reset'))}">${RESET_ICON_SVG}</button>
     </div>`;
@@ -3817,20 +3822,23 @@ function wireSettingRow(def) {
       state.settings[def.key] = color;
       applyTheme(state.settings);
     };
+    const own = () => { delete hex.dataset.inherit; };
     prev.addEventListener('click', async () => {
       const picked = await openColorPicker(prev, hex.value || baseColor(def.key));
-      if (picked) { hex.value = picked.toUpperCase(); apply(picked); }
+      if (picked) { hex.value = picked.toUpperCase(); own(); apply(picked); }
     });
     hex.addEventListener('input', () => {
       const norm = normalizeHex(hex.value, null);
-      if (norm) apply(norm);
+      if (norm) { own(); apply(norm); }
     });
     hex.addEventListener('change', () => {
       const norm = normalizeHex(hex.value, baseColor(def.key));
-      hex.value = norm; apply(norm);
+      hex.value = norm; own(); apply(norm);
     });
     reset.addEventListener('click', () => {
+      // Back to inheriting, not "copy the current admin default in".
       const d = baseColor(def.key);
+      hex.dataset.inherit = '1';
       hex.value = d; apply(d);
     });
   } else if (def.type === 'icon') {
@@ -3860,7 +3868,9 @@ function readAppearanceTable() {
       out[def.key] = el ? el.classList.contains('on') : !!state.settings[def.key];
     } else if (def.type === 'color') {
       const el = document.querySelector(`[data-shex="${def.key}"]`);
-      out[def.key] = normalizeHex(el && el.value, baseColor(def.key));
+      out[def.key] = (el && el.dataset.inherit === '1')
+        ? null                                   // inherit the admin default
+        : normalizeHex(el && el.value, baseColor(def.key));
     } else if (def.type === 'icon') {
       const on = document.querySelector(`[data-sicon="${def.key}"] .group-icon-opt.on`);
       out[def.key] = on ? on.dataset.shareIcon : (state.settings[def.key] || 'share');
diff --git a/frontend/js/version.js b/frontend/js/version.js
index 398f93f..2a1c6d1 100644
--- a/frontend/js/version.js
+++ b/frontend/js/version.js
@@ -1,2 +1,2 @@
 // Increment APP_VERSION with every code change
-export const APP_VERSION = 'v96';
+export const APP_VERSION = 'v97';
diff --git a/frontend/sw.js b/frontend/sw.js
index 8f5809d..d3adc41 100644
--- a/frontend/sw.js
+++ b/frontend/sw.js
@@ -7,7 +7,7 @@
 // the entry HTML / version files). New releases take effect on the next
 // reload, no manual SW unregister required.
 
-const CACHE_VERSION  = 'calendarr-v42';
+const CACHE_VERSION  = 'calendarr-v43';
 const OFFLINE_SHELL  = ['/', '/index.html'];
 
 self.addEventListener('install', event => {