How do I capture the existing color of a group?

Question

My question is a follow-up of my answer to this question Color underline a formula

My answer would have been much better, if I could save the color of the text and then restore it. Is it possible to capture the active color of a group and if yes, how does one do this?

Answer 1

You can save the current color by

\colorlet{currentcolor}{.}

. is just a placeholder for the currently active color. You may choose a name for the color, I just chose currentcolor. Later just use

\color{currentcolor}

Answer 2

Usually we don't have to save the color.

You can try \color@begingroup and \color@endgroup, which is used in LaTeX core heavily. In fact, there is no difference between \begingroup and \color@begingroup, and \color@endgroup is defined as \endgraf\endgroup.

After all, @Stefan's solution is still better in many situations.