Unwanted contour shift for coloured characters

Question

When I'm adding a contour to my coloured maths I get a shifted halo when a \textcolor{} command is encountered. How can this be fixed?

\documentclass[border=2pt]{standalone}
\usepackage[dvipsnames]{xcolor}
\usepackage[outline]{contour}\contourlength{1pt}
\newcommand{\border}[1]{\contour{red}{#1}}
\begin{document}
\border{(F_{!!\infty})}
\border{(\textcolor{white}{F}_{!!\infty})}
\end{document}

Answer 1

You need to avoid having any {} group or color restore after the F otherwise you lose the font metric information on subscript position.

\documentclass[border=2pt]{standalone}
\usepackage[dvipsnames]{xcolor}
\usepackage[outline]{contour}\contourlength{1pt}
\newcommand{\border}[1]{\contour{red}{#1}}
\begin{document}
\border{(F_{!!\infty})}
\border{(\begingroup\color{white}F_{!!\begingroup\color{black}\infty\endgroup}\endgroup)}
\end{document}

Answer 2

With a current latex-dev (What is "latex-dev"?) you can use \mathcolor. (I also use $ $ for the math, that is less fragile). \mathcolor doesn't work yet with xcolor, but will soon:

\documentclass[border=2pt]{standalone}
\usepackage[dvipsnames]{color}
\usepackage[outline]{contour}\contourlength{1pt}
\newcommand{\border}[1]{\contour{red}{#1}}
\begin{document}
\border{(F_{!!\infty})}
\border{$\mathcolor{white}{F}{!!\infty}$}
\border{$\textcolor{white}{F}{!!\infty}$}
\end{document}

Update

contour disables colors locally and this confused \mathcolor. I think this here would be better:

\documentclass[border=2pt]{standalone}
\usepackage{color}
\usepackage[outline]{contour}\contourlength{1pt}
\newcommand{\border}[1]{\contour{red}{#1}}
\makeatletter
\def\con@coloroff{%
   \def\set@color{%
      \c@lor@special\m@ne
        {color push \current@color}\aftergroup\reset@color}%
   \def\reset@color{\c@lor@special\m@ne{color pop}}}
\makeatother
\begin{document}
\border{\(F_{\!\!\infty}\)}
\border{\(\mathcolor{white}{F}_{\!\!\infty}\)}
\border{$\mathcolor{white}{F}_{\!\!\infty}$}
\end{document}