Include darker colors for color output

[cSquaerd]

I noticed that you only allow the bright colors, which are ANSI codes 90 to 96; In the AVAILABLE_COLORS enum in your main file, if additional entries were added with the codes 30 to 36, and their respective keys given something like "dark_" as a prefix, you could double the number of colors offered to users. I might try a pull request if someone else hasn't already, doesn't seem like too big a change.