fix favicon

modules/server/containers/apps/favicon.nix

@@ -26,6 +26,9 @@ let
         paletteValue = lib.attrByPath [ value ] (throw "Unknown favicon color reference `${value}`") palette;
       in
       if builtins.isString paletteValue then
+        if lib.hasPrefix "#" paletteValue then
+          paletteValue
+        else
           "#${paletteValue}"
       else
         throw "favicon palette reference `${value}` must resolve to a string";