Use foreground colors instead of background colors to highlight diffs

[knrafto]

I think foreground colors are more "standard", and the background colors make things unreadable in my color scheme.

Before:

After:

[bjorn3]

Using foreground color would hide whitespace changes, which may be confusing in some cases. If that is a strong enough argument to keep changing the background color, I guess not.

[lnicola]

This bothered me a lot, and it looks much better now. But it might be possible to keep the background color on the whitespace characters, how does that sound?

[knrafto]

I'd rather keep this PR as a small tweak rather than making too many changes to the diffing algorithm (e.g. by detecting significant whitespace changes). How about showing the changes underlined like this?

[knrafto]

Hey, any thoughts on whether this PR should be merged?

[knrafto]

Thanks! 😊