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Why in the second case the spacing is correct and not in the first ?

Maybe not fully correct in the second between + and u ?

enter image description here

\documentclass[xcolor=dvipsnames]{beamer}
    \begin{document}
\begin{frame}
\begin{equation*}
5 \only<1>{\textcolor{red}{+}}6+7
\end{equation*}

  \begin{equation*}
          \frac{\partial u}{\partial t}= \only<1>{\textcolor{red}{+u(n,t)}u(n+1,t)}\only<2>{u(n,t)\textcolor{red}{u(n+1,t)}} -u(n,t)u(n-1,t)
  \end{equation*}

\end{frame}

\end{document}
  • 1
    Compare 5+6+7 with 5{+}6+7. Curly braces around +` (and other math operators) eat space around it. The same happens when you change their color an way as you do. – Zarko Aug 15 '15 at 7:33
  • Thank you, I know now why it doesn't work. How to change the color a math operator ? – Tarass Aug 15 '15 at 7:44
  • the answer is in the comment of this question : tex.stackexchange.com/questions/21598/how-to-color-math-symbols – Tarass Aug 15 '15 at 7:48
  • 1
    One way is manually add the space araound signs, something like {\color{red}\,+\,}. For better way ... temporary I haven't clue. – Zarko Aug 15 '15 at 7:50
  • 2
    A group without making a subformula: \begingroup\color{red}+\endgroup. – Heiko Oberdiek Aug 15 '15 at 7:50

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