Feature request: Custom color themes

[holmanb]

Is your feature request related to a problem? Please describe.
I cannot customize the color palette.

Describe the solution you'd like
I'd love to be able to define on the commandline or in a configuration file which colors to use.

Describe alternatives you've considered
I've tried default, low-contrast, gruvbox, solarized-dark16, solarized-light16. I'd like a low-contrast theme which goes well with my preferred dark terminal. The default is the least offensive to me, but I'd like to have a default which I can fully customize to meet my needs.