I've found time and wrote the patch (it's the file zle_highlight_fix.patch.txt).

With the patch, zle_highlight will be used when user customizes it. If
it's in default state, then termcap will be called for color > 7.

The allows to use zle_highlight entries ( fg_start_code:"code" ... )
for 256-color sequences. This allows to commit the new zle tests,
X04zlehighlight. They're testing region_highlight. The tests are:

0:basic region_highlight with 8 colors
0:basic region_highlight with true-color (hex-triplets)
0:basic region_highlight with near-color (hex-triplets at input)
0:overlapping region_highlight with 8 colors
0:overlapping region_highlight with true-color
0:overlapping region_highlight with near-color (hex-triplets at input)

I can see multiple new tests being added.

On Fri, 21 Dec 2018 at 06:40, Sebastian Gniazdowski
<sgniazdowski@gmail.com> wrote:
>
> Could this wait for the (todays?) patch where zle_highlight is used
> only when it is set to other than default value?
> This would fix rather most certainly a bug. This would allow to add
> X04zlehighlight tests.
>
> BTW. I've submitted an issue to iTerm2, there are people that know
> much about terminals, and it yielded a few interesting facts:
> https://gitlab.com/gnachman/iterm2/issues/7221
>
> On Wed, 19 Dec 2018 at 21:56, Peter Stephenson
> <p.w.stephenson@ntlworld.com> wrote:
> >
> > I've uploaded a test version of zsh to
> >
> > http://www.zsh.org/pub/development/
> >
> > Not much particularly likely to be amiss.  However, unless everyone is
> > prepared to swear blind within a day or so that it's OK it'll probably
> > be the new year before I get a chance to make a release.
> >
> > pws
> >
> >
>
>
> --
> Sebastian Gniazdowski
> News: https://twitter.com/ZdharmaI
> IRC: https://kiwiirc.com/client/chat.freenode.net:+6697/#zplugin
> Blog: http://zdharma.org



-- 
Sebastian Gniazdowski
News: https://twitter.com/ZdharmaI
IRC: https://kiwiirc.com/client/chat.freenode.net:+6697/#zplugin
Blog: http://zdharma.org