[LyX/master] Change preedit color settings

[Jürgen Spitzmüller]

Am Samstag, dem 04.07.2026 um 19:07 +0200 schrieb Jürgen Spitzmüller:
> Am Samstag, dem 04.07.2026 um 16:25 +0200 schrieb Scott Kostyshak:
> > Starting with this commit, my cursor turns black when it enters a
> > math
> > inset. I am using dark mode, in case it is relevant.
> > 
> > Can anyone reproduce?
> 
> Yes. The reason is that math background has been set to transparent,
> but the cursor inversion code relies on it being a non-transparent
> color to determine whether it is dark or light.

It turned the foreground/background optimization I have recently added
has been broken by transparent color support.

I did what I could and have fixed the obvious cases. It is well
possible that there are more bugs to discover. 

-- 
Jürgen