Breaks compatibility with terminal color-names.

[mikenrafter]

PyWal, when generating a theme from a background image, breaks color names.

For example, in my config.fish, I've set my username to be shown as blue. However, with this particular colorscheme, see what happens?:

I think that color names should be somewhat respected, or at least an option given to force them to be respected by a threshold value of some sort.

[mikenrafter]

Potentially similar/duplicate? #619