support different colors or maybe a -dark option or something

[j256]

I'm am loving terminal-velocity so thanks so much for it. My problem is that I've had to change the default colors because I run in white on black terminal windows. I use light blue instead of dark and white instead of black in the palette map. I've not seen anything in the docs which indicates that I can set these colors in the configs.

And sorry but I'm not a python hacker so I can't submit a PR.