Add option to not change foreground color when --bg is active

[sandstripes]

Currently, the foreground color is changed when --bg is active. On short text, this causes the text color to sometimes abruptly change halfway, and I wish to be able to turn this off.

[magnus-ISU]

I think this is done to try to make the highest-contrast text possible. However, in that example it does look weird. I'll see what I can do.