nixos-icons: recolor white logo (#297)

Fixes #292

modules/nixos-icons/nixos.nix

@@ -0,0 +1,24 @@
+{ pkgs, config, lib, ... }:
+
+with config.lib.stylix.colors;
+
+{
+  options.stylix.targets.nixos-icons.enable =
+    config.lib.stylix.mkEnableTarget "the NixOS logo" true;
+
+  config.nixpkgs.overlays = lib.mkIf config.stylix.targets.nixos-icons.enable [(self: super: {
+    nixos-icons = super.nixos-icons.overrideAttrs (oldAttrs: {
+      patchPhase = ''
+        substituteInPlace logo/white.svg --replace-fail '#ffffff' '#${base05}'
+
+        # Insert attribution comment after the XML prolog
+        sed \
+          --in-place \
+          '2i<!-- The original NixOS logo from ${oldAttrs.src.url} is licensed under https://creativecommons.org/licenses/by/4.0 and has been modified to match the ${scheme} color scheme. -->' \
+          logo/white.svg
+
+        ${lib.getExe pkgs.resvg} logo/white.svg logo/white.png
+      '';
+    });
+  })];
+}