Feature request: add theme for terminals with white backgroud

[xtavras]

Right now, if you use terminal with light color background, you see almost nothing. Would be cool if you can switch to using black color for processes and network utilization.

[ncfavier]

Other options include:

• let the table rows use the default foreground colour instead of Color::White (see Use default foreground color instead of white #65),
• provide a way to disable colours entirely.