cross symbol over a mathematical term

Question

I am writing a presentation with beamer

\documentclass[a4paper]{beamer}
\usepackage{amsmath}
\begin{document}
\begin{frame}
\[\hat{H}=\sum(-\frac{\nabla_i^2}{2m})+\sum(-\frac{\nabla_i^2}{2M})+\dots\]
\end{frame}
\end{document}

Now, I want to show in my presentation that we can ignore the 2nd term \sum(-\frac{\nabla_i^2}{2M}) possibly putting a cross over it. So, in the next frame, I will like to have

\[\hat{H}=\sum(-\frac{\nabla_i^2}{2m})+
\A_RED_CROSS_OVER_THIS_TERM{\sum(-\frac{\nabla_i^2}{2M})}+\dots\]

Is this possible?

EDIT

\documentclass[a4paper]{beamer}
\usepackage{amsmath,color}
\definecolor{red}{RGB}{255,127,0}
\usepackage[makeroom]{cancel}
\renewcommand{\CancelColor}{red}
\begin{document}
\begin{frame}
  \[\hat{H}=\sum(-\frac{\nabla_i^2}{2m})+\xcancel{\sum(-\frac{\nabla_i^2}{2M})}+\dots\]
\end{frame}
\end{document}

Tried this, and color has not changed.

Answer 1

The definition of \CancelColor does not take a color but a color command:

\documentclass[a4paper]{beamer}
\usepackage{amsmath,color}
\definecolor{red}{RGB}{255,127,0}
\usepackage[makeroom]{cancel}
\renewcommand{\CancelColor}{\color{red}}
\begin{document}
\begin{frame}
  \[\hat{H}=\sum(-\frac{\nabla_i^2}{2m})+\xcancel{\sum(-\frac{\nabla_i^2}{2M})}+\dots\]
\end{frame}
\end{document}

Answer 2

\documentclass[a4paper]{beamer}
\usepackage{stackengine}
\usepackage{scalerel}
\usepackage{amsmath,color}
\definecolor{red}{RGB}{255,127,0}
\begin{document}
\def\x{\displaystyle\sum(-\frac{\nabla_i^2}{2M})}
\begin{frame}
  \[\hat{H}=\sum(-\frac{\nabla_i^2}{2m})+\stackengine{-.3ex}{$\x$}%
{\hstretch{3}{\scalerel*{\textcolor{red}{\times}}{\x}}}%
{O}{c}{F}{T}{L}%
+\dots\]
\end{frame}
\end{document}

One advantage to using this approach is that the crossout material can be anything. Changing the \hstretch from 3 to 0.6 and changing \times to something else gives

Make sure you have V2.0 of stackengine, available at ctan.org