diff --git a/docs/EXTENSIONS.md b/docs/EXTENSIONS.md
index a53fcf38..59d0de53 100644
--- a/docs/EXTENSIONS.md
+++ b/docs/EXTENSIONS.md
@@ -351,15 +351,18 @@ written into CSS, every value is sanitized in core, once, so every theme
 extension inherits the guard:
 
 - **Allowed token names** (anything else is dropped): `--bg`, `--surface`,
-  `--surface2`, `--text`, `--text2`, `--muted`, `--accent`, `--accent2`,
-  `--accent3`, `--accent-contrast`, `--border`, `--border2`, `--hover-bg`,
-  `--code-bg`, `--code-text`, `--sidebar`, `--sidebar-text`, `--user-bubble`,
-  `--assistant-bubble`, `--success`, `--warning`, `--danger`, `--info`, `--link`.
+  `--surface2`, `--surface-subtle`, `--text`, `--text2`, `--muted`, `--accent`,
+  `--accent2`, `--accent3`, `--accent-contrast`, `--accent-hover`,
+  `--accent-text`, `--accent-bg`, `--accent-bg-strong`, `--accent-rgb`,
+  `--border`, `--border2`, `--hover-bg`, `--code-bg`, `--code-text`,
+  `--sidebar`, `--sidebar-text`, `--user-bubble`, `--assistant-bubble`,
+  `--success`, `--warning`, `--danger`, `--info`, `--link`.
 - **Allowed value shapes** (anything else is dropped): hex colors, `rgb()` /
-  `rgba()`, `hsl()` / `hsla()`, CSS color keywords, and simple
-  numeric-with-unit values (`px`/`em`/`rem`/`%`). Values containing `url()`,
-  `expression()`, semicolons, braces, or other CSS-injection vectors are
-  rejected.
+  `rgba()`, `hsl()` / `hsla()`, CSS color keywords, simple numeric-with-unit
+  values (`px`/`em`/`rem`/`%`), and a bare RGB triple (e.g. `0, 0, 0` for
+  `--accent-rgb`, which the app consumes inside `rgba(...)`). Values containing
+  `url()`, `expression()`, semicolons, braces, or other CSS-injection vectors
+  are rejected.
 - **Reserved keys are protected** — an extension cannot overwrite a built-in
   skin key (e.g. `default`, `ares`, `graphite`).
 - A descriptor with no valid tokens after sanitization is rejected entirely.
diff --git a/static/boot.js b/static/boot.js
index 03c67e99..b4f065e0 100644
--- a/static/boot.js
+++ b/static/boot.js
@@ -2013,15 +2013,17 @@ const _RESERVED_SKIN_KEYS=new Set((_SKINS||[]).map(s=>(s.value||s.name).toLowerC
 // CSS custom-property names a skin is allowed to set. Mirrors the documented
 // design-token contract; anything outside this set is dropped.
 const _ALLOWED_SKIN_TOKENS=new Set([
-  '--bg','--surface','--surface2','--text','--text2','--muted',
-  '--accent','--accent2','--accent3','--accent-contrast',
+  '--bg','--surface','--surface2','--surface-subtle','--text','--text2','--muted',
+  '--accent','--accent2','--accent3','--accent-contrast','--accent-hover',
+  '--accent-text','--accent-bg','--accent-bg-strong','--accent-rgb',
   '--border','--border2','--hover-bg','--code-bg','--code-text',
   '--sidebar','--sidebar-text','--user-bubble','--assistant-bubble',
   '--success','--warning','--danger','--info','--link'
 ]);
-// Accept only safe color / simple numeric-with-unit values. Rejects anything
+// Accept only safe color / simple numeric-with-unit values, OR a bare RGB triple
+// (e.g. "0, 0, 0" for --accent-rgb, consumed inside rgba(...)). Rejects anything
 // with url(), expression(), semicolons, braces, or other CSS-injection vectors.
-const _SAFE_SKIN_VALUE_RE=/^(#(?:[0-9a-fA-F]{3,8})|rg(?:b|ba)\(\s*[0-9.,%\s/]+\)|hsl(?:a)?\(\s*[0-9.,%\s/deg]+\)|[a-zA-Z]{3,20}|[0-9.]+(?:px|em|rem|%)?)$/;
+const _SAFE_SKIN_VALUE_RE=/^(#(?:[0-9a-fA-F]{3,8})|rg(?:b|ba)\(\s*[0-9.,%\s/]+\)|hsl(?:a)?\(\s*[0-9.,%\s/deg]+\)|[0-9]{1,3}\s*,\s*[0-9]{1,3}\s*,\s*[0-9]{1,3}|[a-zA-Z]{3,20}|[0-9.]+(?:px|em|rem|%)?)$/;
 
 function _sanitizeSkinTokens(tokens){
   const out={};
@@ -2299,17 +2301,26 @@ window._applyTitlebarProfileVisibility=_applyTitlebarProfileVisibility;
     const lsTheme=(localStorage.getItem('hermes-theme')||'').trim().toLowerCase();
     const lsSkin=(localStorage.getItem('hermes-skin')||'').trim().toLowerCase();
     const lsAppearance=_normalizeAppearance(lsTheme||null,lsSkin||null);
+    // An unknown non-default persisted skin is most likely an extension-provided
+    // skin (registerHermesSkin) whose extension script hasn't registered it yet
+    // at this point in boot. Preserve it verbatim instead of normalizing it away
+    // to 'default' — the extension's registerHermesSkin() will inject the CSS and
+    // re-apply it once it loads. Without this, the boot sync would clobber the
+    // saved choice before the extension runs.
+    const lsSkinIsPendingExt=!!lsSkin&&lsSkin!=='default'&&!_VALID_SKINS.has(lsSkin)&&!_LEGACY_THEME_MAP[lsSkin];
     const lsHasExplicitSkin=lsSkin&&lsSkin!=='default';
     const lsHasExplicitTheme=lsTheme&&['system','light','dark'].includes(lsTheme);
     const theme=lsHasExplicitTheme?lsAppearance.theme:srvAppearance.theme;
-    const skin=lsHasExplicitSkin?lsAppearance.skin:srvAppearance.skin;
+    const skin=lsHasExplicitSkin?(lsSkinIsPendingExt?lsSkin:lsAppearance.skin):srvAppearance.skin;
     localStorage.setItem('hermes-theme',theme);
     _applyTheme(theme);
     localStorage.setItem('hermes-skin',skin);
     _applySkin(skin);
     // Reconcile: if localStorage and server disagree, push localStorage
-    // values to the server so the next refresh won't revert.
-    if((lsHasExplicitTheme||lsHasExplicitSkin)&&(theme!==srvAppearance.theme||skin!==srvAppearance.skin)){
+    // values to the server so the next refresh won't revert. Skip the push for a
+    // still-pending extension skin (don't persist it server-side until it's a
+    // confirmed-registered skin — avoids writing a skin the server can't validate).
+    if((lsHasExplicitTheme||lsHasExplicitSkin)&&!lsSkinIsPendingExt&&(theme!==srvAppearance.theme||skin!==srvAppearance.skin)){
       try{
         api('/api/settings',{method:'POST',body:JSON.stringify({theme,skin})});
       }catch(_){}
diff --git a/static/index.html b/static/index.html
index e63669b5..8287fc6a 100644
--- a/static/index.html
+++ b/static/index.html
@@ -17,7 +17,7 @@
 <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
 <meta name="apple-mobile-web-app-title" content="Hermes">
 <link rel="apple-touch-icon" sizes="512x512" href="static/apple-touch-icon.png">
-<script>(function(){try{var themes={light:1,dark:1,system:1},skins={codex:1,terracotta:1,default:1,ares:1,mono:1,graphite:1,github:1,slate:1,poseidon:1,sisyphus:1,charizard:1,sienna:1,catppuccin:1,hepburn:1,nous:1,'geist-contrast':1,neon:1,zeus:1,'verdigris':1},legacy={slate:['dark','slate'],solarized:['dark','poseidon'],monokai:['dark','sisyphus'],nord:['dark','slate'],oled:['dark','default']},t=(localStorage.getItem('hermes-theme')||'dark').toLowerCase(),s=(localStorage.getItem('hermes-skin')||'').toLowerCase(),m=legacy[t],theme=m?m[0]:(themes[t]?t:'dark'),skin=skins[s]?s:(m?m[1]:'default');localStorage.setItem('hermes-theme',theme);localStorage.setItem('hermes-skin',skin);if(theme==='system')theme=window.matchMedia('(prefers-color-scheme:dark)').matches?'dark':'light';if(theme==='dark')document.documentElement.classList.add('dark');if(skin!=='default')document.documentElement.dataset.skin=skin;}catch(e){document.documentElement.classList.add('dark');}})()</script>
+<script>(function(){try{var themes={light:1,dark:1,system:1},skins={codex:1,terracotta:1,default:1,ares:1,mono:1,graphite:1,github:1,slate:1,poseidon:1,sisyphus:1,charizard:1,sienna:1,catppuccin:1,hepburn:1,nous:1,'geist-contrast':1,neon:1,zeus:1,'verdigris':1},legacy={slate:['dark','slate'],solarized:['dark','poseidon'],monokai:['dark','sisyphus'],nord:['dark','slate'],oled:['dark','default']},t=(localStorage.getItem('hermes-theme')||'dark').toLowerCase(),s=(localStorage.getItem('hermes-skin')||'').toLowerCase(),m=legacy[t],theme=m?m[0]:(themes[t]?t:'dark');var pendingExt=s&&s!=='default'&&!skins[s]&&!legacy[s];var skin=skins[s]?s:(pendingExt?s:(m?m[1]:'default'));localStorage.setItem('hermes-theme',theme);localStorage.setItem('hermes-skin',skin);if(theme==='system')theme=window.matchMedia('(prefers-color-scheme:dark)').matches?'dark':'light';if(theme==='dark')document.documentElement.classList.add('dark');if(skin!=='default')document.documentElement.dataset.skin=skin;}catch(e){document.documentElement.classList.add('dark');}})()</script>
 <script>(function(){try{var fs=localStorage.getItem('hermes-font-size');if(fs&&fs!=='default')document.documentElement.dataset.fontSize=fs;}catch(e){}})()</script>
 <!-- theme-color: surfaces the active app chrome color to native status bars (Safari status bar, PWA, native WKWebView wrappers). Updated dynamically by boot.js when theme/skin changes. The light/dark default values match style.css :root --sidebar / :root.dark --sidebar. -->
 <meta name="theme-color" content="#FAF7F0" media="(prefers-color-scheme: light)">
diff --git a/tests/test_extension_theme_registration.py b/tests/test_extension_theme_registration.py
index 64658a1f..ad92b25e 100644
--- a/tests/test_extension_theme_registration.py
+++ b/tests/test_extension_theme_registration.py
@@ -45,6 +45,31 @@ def test_reserved_core_skins_are_guarded():
     )
 
 
+def test_pending_extension_skin_is_preserved_across_boot():
+    """A persisted skin that isn't a known core skin (i.e. an extension skin
+    not yet registered at boot) must NOT be clobbered to 'default' by the
+    boot-time appearance sync, or it won't survive a reload."""
+    assert "lsSkinIsPendingExt" in BOOT_JS, (
+        "boot sync must detect a pending (unregistered) extension skin"
+    )
+    # the boot sync must keep the raw ls value for a pending ext skin
+    assert "lsSkinIsPendingExt?lsSkin:lsAppearance.skin" in BOOT_JS, (
+        "boot sync must preserve the raw pending-ext skin instead of normalizing it away"
+    )
+
+
+INDEX_HTML = (REPO / "static" / "index.html").read_text(encoding="utf-8")
+
+
+def test_prepaint_inline_script_preserves_unknown_skin():
+    """The pre-paint inline script in index.html must also preserve an unknown
+    persisted skin (a likely extension skin) rather than resetting localStorage
+    to 'default' before boot.js / the extension runs."""
+    assert "pendingExt" in INDEX_HTML, (
+        "pre-paint script must detect a pending extension skin and keep it"
+    )
+
+
 # ── Layer 2: behavioral (Node harness drives the real functions) ─────────────
 
 _HARNESS = r"""