cancel with different colors

The color of the line used by cancel can be changed with

\renewcommand\CancelColor{<color command>}

You could include this in a new cancel-command where an optional argument defines the color.

\documentclass{article}
\usepackage{cancel}
\usepackage{xcolor}
\newcommand\Ccancel[2][black]{\renewcommand\CancelColor{\color{#1}}\cancel{#2}}

\begin{document}
\[
\Ccancel{x+1} \qquad \Ccancel[blue]{x-1}
\]
\end{document}