[REQUEST] Ability to specify themes using cterm/ansi colors (0-15)

[graelo]

Thanks for the great app!

Is your feature request related to a problem? Please describe.
In the themes, it seems that btop++ allows only hardcoded colors codes, and unless I missed something, cterm/ansi color codes are not supported.

Describe the solution you'd like
I'd love btop to allow loading themes where colors are (0-15), e.g.

# theme[main_bg]="#fdf6e3"
theme[main_bg]="15"  # white in solarized light

Describe alternatives you've considered
I would have to define the two themes (dark/light) and a symlink to the current one, and when switching my terminal palette, I would also update the symlink and relaunch btop++.

Additional context
A benefit of using 16-color terminals is that changing the terminal's palette instantly changes the appearance of all terminal apps, as long as they express their theme using ansi/cterm colors.

WDYT?
Thanks in advance!
Best