Commandline option: background colour?

[rubyFeedback]

I tried this:

rb topinambour  --execute bash --background=black

in bin/

The first works, I can use bash upon starting it. The second is not supported.

I understand that via CSS we can modify that, but perhaps we could also add
such commandline option, to have black background? Right now the default
for me here seems to be a darkish gray. Anyway this is not so important,
just wanted to suggest it. :)