highlight: fix color type

The color options also allow color definitions in the form of color names.

docs/release-notes/rl-0.8.md

@@ -338,6 +338,7 @@
 - Add missing `flutter-tools.nvim` dependency `plenary.nvim`.
 - Add necessary dependency of `flutter-tools.nvim` on lsp.
 - Add the `vim.languages.dart.flutter-tools.flutterPackage` option.
+- Fix the type of the `highlight` color options.
 
 [howird](https://github.com/howird):
 

modules/neovim/init/highlight.nix

@@ -5,15 +5,14 @@
 }: let
   inherit (lib.options) mkOption;
   inherit (lib.types) nullOr attrsOf listOf submodule bool ints str enum;
-  inherit (lib.strings) hasPrefix concatLines;
+  inherit (lib.strings) concatLines;
   inherit (lib.attrsets) mapAttrsToList;
   inherit (lib.nvim.dag) entryBetween;
   inherit (lib.nvim.lua) toLuaObject;
-  inherit (lib.nvim.types) hexColor;
 
   mkColorOption = target:
     mkOption {
-      type = nullOr hexColor;
+      type = nullOr str;
       default = null;
       example = "#ebdbb2";
       description = ''