Phil wrote
> However, it would seem that while the "xdv2pdf" driver was happy with
\special {color push}, the "xdvipdfmx" driver is not.I doubt that ever worked, the semantics of "push" on any stack mean you have to say what you are putting on the stack, unlike pop where you just take off the top element (or underflow) most of the color specials are in section 7 of texdoc dvipdfm, but that has a different syntax for its colour stack push/pop (the begincolor (bc) special which isn't used in the latex back end at all) I don't suppose you count the most reliable documentation? https://github.com/TeX-Live/texlive-source/blob/trunk/texk/dvipdfm-x/spc_color.c#L167
