Interesting ... this seemed to work at first for me, but further testing 
seems to turn up an issue as well.
If I try to specify a colour for the non-match part of the pattern, then 
for `a -><tab>` I *do* see the description in red, but the non-match 
part isn't coloured ... for the other test cases (`a --` & b & c) it 
does show both colors correctly.

Screenshot: 
https://cloud.githubusercontent.com/assets/168694/25103774/0a3122f0-23be-11e7-9ded-ef60067621a7.png

On 17 Apr 2017, at 20:05, Daniel Shahaf wrote:

> apfelsinenhain@gmx.de wrote on Mon, Apr 17, 2017 at 19:02:15 +0200:
>>> zstyle ':completion:*' list-separator "XX"
>>> zstyle ':completion:*:default' list-colors '=XX*=31'
>>
>> - try:
>>   - `a -<tab>`  WILL show color
>>   - `a --<tab>` will NOT show color
>
> Not sure whether it's a bug, but this setting seems to work:
>
>     zstyle ':completion:*:default' list-colors '=(#b)*(XX*)==31'