> Juri> Yellow foreground works well for context lines.
> Except when you normally read black on white.
For quite a long time (most likely from the time when color translation
was implemented for tty) colors of context lines in diff mode on tty
were yellow for light backgrounds. There are also other faces with
yellow foreground for light backgrounds, like font-lock-variable-name-face.
Nobody complained about them so far. So maybe yellow is the acceptable
color for context lines.
> Is there no way to switch automatically to a proper set of darker
> colors when the main text is black instead of white?
By default on terminals Emacs background mode is `light', regardless of
actual terminal background color, so you don't need to change the
background mode when the main text is black on white.