Daniel Martín via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs@gnu.org> writes:

>>
>> Thanks.  But I think the use of static variables there is rather ugly,
>> and it would be much nicer if we replicated the `x_setup_relief_color'
>> logic there.
>>
>> Do you want to work on that, or should I?
>
> Thanks, I can give it a try.

Here's a patch where the static variables are now proper fields in the
ns_output structure.  Is that what you had in mind?