FR: expose color values for arbitrary usage

While Ports are more holistic, it would increase ease of adoption if I could do something like this ```nix { catppuccin-raw, ... }: let ctp = catppuccin-raw.colors; in { catppuccin-raw.theme = "mocha"; catppuccin-raw.accent = "lavender"; program.foobar.theme = { primary = ctp.base; accent = ctp.accent; }; } ```