bug#43702: Emacs master: Incorrect highlighting in regexp isearch.

[Drew Adams <drew.adams@oracle.com>]

> >> Even the color scheme designed by Drew has problems.
> >
> > What problems?
> 
> On the screenshot you sent it's hard to tell 3 from 7,
> 1 from 5, 2 from 6, 4 from 8.

It's intentional.  I explained why it's not a
problem in practice.  Few regexps use more than
4 groups.

1. Groups near each other, in group order, are
   easily distinguishable, regardless of where
   they are in the list.  E.g., (2,3,4), (4,5 6),
   or (8,1,2).

2. Most important is distinguishing groups 1-4,
   without using faces that are too in-your-face
   or conflict with most other highlighting.

3. Hue, at the same saturation & value, is the
   best way to distinguish without violating #2.

4. Groups 5-8 are paler and more rarely used.
   Their differences need not be as pronounced
   as 1-4.

But as you say, being able to customize is what's
most important.

And by doing so, to, in effect, shrink the number of
faces in the cycle (by using identical definitions).