Is there a way to color (only real) math in pdflatex?

Question

I'd like to change the color of all math in my document. I understand that several packages and some engines provide support for changing the color of all math, and I understand that something like

\everymath{\color{green}}

almost works, but also ends up coloring things like URLs and captions, while failing to color displayed equations.

Is there a reliable way to change the color of just math, in pdflatex, without relying on special packages or classes?

Answer 1

\everymath{\color{green}}
\everydisplay{\color{green}}
\def\m@th{\normalcolor\mathsurround\z@}

will get you most of the way there, although you are still likely to need some special fixup for individual commands here and there that use math internally without using the \m@th command which I redefine above to reset the color. Most "internal" uses of math for vertical centering tables or superscripting footnote marks etc, use that macro but that convention (from Plain TeX originally) is not enforced anywhere, and also redefining it might not be safe in all contexts (\edef for example) so some uses may need more explicit redefinitions to reset the colour.