\begingroup messes up spacing

this is a standard issue in latex, see e.g.
https://tex.stackexchange.com/questions/85033/colored-symbols/85035#85035
try the following
```
\begin{gathered}
U \oplus V\\
U {\color{red}\oplus} V\\
U\begingroup\color{red}\oplus\endgroup V
\end{gathered}
```
in LaTeX vs KaTeX. in LaTeX the 2nd has wrong spacing, but the third line is okay; in KaTeX both 2nd and 3rd lines are incorrect.