Fix tooltips' white font on light color schemes

White colored font was unreadable rendering tooltips useless. I think green is the most appropriate one for text here (rationale: some messages are already green, it looks good on both light and dark versions of most color schemes). Anyhow, it is much better than leaving white as it is now.

EDIT: another option is leaving font colour to be handled by a colour scheme.

@teams/vdg

Before:

After:

After the 2nd commit:

BUG: 442250