diff --git a/src/govoplan_access/backend/api/v1/auth.py b/src/govoplan_access/backend/api/v1/auth.py
index 7ce24ce..d2b6353 100644
--- a/src/govoplan_access/backend/api/v1/auth.py
+++ b/src/govoplan_access/backend/api/v1/auth.py
@@ -16,6 +16,7 @@ from govoplan_core.api.v1.schemas import (
     AuthShellResponse,
     AuthSessionResponse,
     AuthSessionUserInfo,
+    EffectiveAppearanceInfo,
     GroupInfo,
     LoginRequest,
     LoginResponse,
@@ -31,6 +32,7 @@ from govoplan_core.api.v1.schemas import (
     UserUiPreferences,
 )
 from govoplan_core.core.access import AuthMethod, PrincipalRef
+from govoplan_core.core.appearance import resolve_effective_appearance
 from govoplan_core.core.identity import CAPABILITY_IDENTITY_DIRECTORY, IdentityDirectory
 from govoplan_core.core.registry import PlatformRegistry
 from govoplan_core.core.principal_cache import invalidate_auth_principals
@@ -255,12 +257,23 @@ def _user_ui_preferences(settings_payload: object) -> UserUiPreferences:
         return UserUiPreferences()
 
 
+def _effective_appearance_info(session: Session, *, tenant: Tenant, user: User) -> EffectiveAppearanceInfo:
+    system_item = get_system_settings(session)
+    decision = resolve_effective_appearance(
+        system_settings=system_item.settings,
+        tenant_settings=tenant.settings,
+        user_settings=user.settings,
+    )
+    return EffectiveAppearanceInfo.model_validate(decision.as_dict())
+
+
 def _user_info(
     user: User,
     account: Account,
     *,
     preferred_language: str | None = None,
     enabled_language_codes: list[str] | None = None,
+    appearance: EffectiveAppearanceInfo | None = None,
 ) -> UserInfo:
     return UserInfo(
         id=user.id,
@@ -273,6 +286,7 @@ def _user_info(
         preferred_language=preferred_language,
         enabled_language_codes=enabled_language_codes or [],
         ui_preferences=_user_ui_preferences(user.settings),
+        appearance=appearance or EffectiveAppearanceInfo(),
     )
 
 
@@ -593,7 +607,7 @@ def _shell_response(
         ]
     )
     return AuthShellResponse(
-        user=_user_info(user, account),
+        user=_user_info(user, account, appearance=_effective_appearance_info(session, tenant=tenant, user=user)),
         tenant=active_tenant,
         active_tenant=active_tenant,
         tenants=memberships,
@@ -669,6 +683,7 @@ def _profile_response(session: Session, context: AuthContext) -> AuthProfileResp
             context.account,
             preferred_language=preferred_language,
             enabled_language_codes=user_enabled,
+            appearance=_effective_appearance_info(session, tenant=context.tenant, user=context.user),
         ),
         tenant=active_tenant,
         active_tenant=active_tenant,
@@ -783,7 +798,13 @@ def _me_response(
         )
     ]
     return MeResponse(
-        user=_user_info(user, account, preferred_language=preferred_language, enabled_language_codes=user_enabled),
+        user=_user_info(
+            user,
+            account,
+            preferred_language=preferred_language,
+            enabled_language_codes=user_enabled,
+            appearance=_effective_appearance_info(session, tenant=tenant, user=user),
+        ),
         tenant=active_tenant,
         active_tenant=active_tenant,
         tenants=memberships,
@@ -991,6 +1012,17 @@ def update_profile(
         if payload.ui_preferences is None:
             next_settings["ui"] = UserUiPreferences().model_dump()
         else:
+            appearance = _effective_appearance_info(session, tenant=context.tenant, user=context.user)
+            stored_palette = _user_ui_preferences(context.user.settings).palette
+            if (
+                appearance.locked
+                and payload.ui_preferences.palette is not None
+                and payload.ui_preferences.palette != stored_palette
+            ):
+                raise HTTPException(
+                    status_code=status.HTTP_422_UNPROCESSABLE_CONTENT,
+                    detail="The effective appearance policy locks the palette.",
+                )
             if (
                 payload.ui_preferences.navigation is not None
                 and payload.ui_preferences.navigation.locked
diff --git a/src/govoplan_access/backend/manifest.py b/src/govoplan_access/backend/manifest.py
index 17ce8b2..187a561 100644
--- a/src/govoplan_access/backend/manifest.py
+++ b/src/govoplan_access/backend/manifest.py
@@ -301,6 +301,25 @@ ADMIN_READ_SCOPES = (
 )
 
 ACCESS_DOCUMENTATION: tuple[DocumentationTopic, ...] = (
+    DocumentationTopic(
+        id="access.reference.effective-appearance",
+        title="Understand the effective appearance source",
+        summary="The authenticated profile explains whether the active palette comes from the user, tenant, system, or a policy lock.",
+        body=(
+            "An explicit personal palette normally wins over tenant and system defaults. "
+            "Resetting it stores inheritance, not a copy of the current default. A tenant "
+            "policy lock suppresses personal choices; a system lock suppresses both tenant "
+            "and personal choices. Access enforces the lock during profile writes and returns "
+            "the effective palette, source, inherited value, and lock state on full profile responses."
+        ),
+        layer="always",
+        documentation_types=("admin", "user"),
+        audience=("user", "tenant_admin", "system_admin"),
+        order=8,
+        links=(DocumentationLink(label="Profile API", href="/api/v1/auth/profile", kind="api"),),
+        related_modules=("admin", "tenancy"),
+        metadata={"kind": "reference", "help_contexts": ["core.settings", "admin.system-settings", "tenancy.admin.tenant-settings"]},
+    ),
     DocumentationTopic(
         id="access.reference.resource-explanation-subjects",
         title="Select a user for resource-access diagnostics",