RE: [PATCH] isearch: lazy-highlighting of sub-exps of regexps

[Drew Adams]

> > I picked the default colors by tweaking (using palette.el). 
> > I picked the dark-background colors by starting with the
> > complements of the light-background colors (and then
> > modifying a bit, IIRC).  I probably got some user feedback on
> > the dark-background colors (I use a light background, 
> > myself), but I don't remember.
> 
> I'm tempted to try a rainbow, because it has a very intuitive palette.

FWIW, I deliberately did not do that.

Successive levels should have colors that are quite distinctive; otherwise it
can be more difficult to distinguish their boundaries.  IOW, instead of red
yellow green cyan blue magenta, mix it up so that near hues are not adjacent:
cyan is not next to green or blue, etc.

The order, in the sense of group level, is not significant (helpful).  If it
were, then you could perhaps argue in favor of rainbow order: Seeing green you
could look for cyan as the next level (numerically) etc.

All that is important in terms of matching is visual distinction: telling where
one match ends and the next (adjacent) one begins; that is, distinguishing one
group from another. Cyan is easier to distinguish from red, yellow, or magenta
than it is from green or blue.

But arguments are one thing.  Another is to experiment.