How to prevent xcolor from influencing algebraic sign spacing?

Question

The xcolor package influences the spacing of the algebraic sign. How to prevent this behavior?

Screenshot

Mathematical background

The second example should be treated as a binary operator instead of an unary operator.

See: Unary vs. binary operator spacing in LaTeX

MWE

\documentclass{scrreprt}

\usepackage{xcolor}

\begin{document}
\(1 + 2\)

\(1 {\color{gray} + 2}\)

\end{document}

Workaround

By manually adjusting the spacing...

\(1 {\color{gray}\,+\,2}\)

Answer 1

An explicit brace group creates a sub_mlist which will always be assigned class mathord (if I'm not mistaken). You can easily work around that problem by just using \begingroup...\endgroup instead of braces.

\documentclass{scrreprt}

\usepackage{xcolor}

\begin{document}
\(1 + 2\)

\(1 \begingroup\color{gray} + 2\endgroup\)

\end{document}

Answer 2

The problem is not the color but the group:

\documentclass{scrreprt}

\usepackage{xcolor}

\begin{document}
\(1 + 2\)

\(1 {+ 2}\)

\(1 {{} + 2}\)

\(1 {\color{gray} + 2}\)

\(1 {\color{gray}{} + 2}\)

\end{document}