Mathtools and Tikz are incompatible because of colon

Question

I tried to use tikz and https://tex.stackexchange.com/a/270007/161413 to color arrows with several colors. But I was also using mathtools, and found out that tikz and mathtools are not compatible as they both change the definition of :.

I applied the solution in https://tex.stackexchange.com/a/89470/161413 but still it does not work.

Here is my MWE (I am using XeLaTeX):

\documentclass{article}
\usepackage[
a4paper,
margin=30mm
]{geometry}
\usepackage{amsmath, amssymb, amsthm}
\usepackage{tikz}
\usepackage{mathtools} % commenting this line works
\usepackage{etoolbox}
\makeatletter
\AtEndPreamble{
    \ifnum\mathcode\:=\string"8000 \begingroup\lccode~=\: \lowercase{\endgroup\let\math@colon@meaning~} \else \expandafter\let\expandafter\math@colon@meaning\string: \fi } \AtBeginDocument{ \ifnum\catcode:=\active
    \letcs\text@colon@meaning{active@char\string:}
    \else
    \expandafter\let\expandafter\text@colon@meaning\string:
    \fi
    \protected\def\tikz@nonactivecolon{%
        \ifmmode
        \expandafter\math@colon@meaning
        \else
        \expandafter\text@colon@meaning
        \fi} 
    \begingroup\lccode\~=:
    \lowercase{\endgroup\let~\tikz@nonactivecolon}
}
\makeatother
\usetikzlibrary{graphs}
\usetikzlibrary{positioning}
\usetikzlibrary{intersections}
\usetikzlibrary{decorations.markings}
\newlength\mylen
\tikzset{
    bicolor/.style n args={2}{
        decoration={
            markings,
            mark=at position 0.5 with {
                \node[draw=none,inner sep=0pt,fill=none,text width=0pt,minimum size=0pt] {\global\setlength\mylen{\pgfdecoratedpathlength}};
            },
        },
        draw=#1,
        dash pattern=on 0.5\mylen off 0.5\mylen,
        preaction={decorate},
        postaction={
            draw=#2,
            dash pattern=on 0.5\mylen off 0.5\mylen,dash phase=0.5\mylen
        },
    }
}
\begin{document}
\begin{tikzpicture}
\node (bbb) at (0,0) {bbb};
\node (baa) at (150:3) {baa};
\draw[->, bicolor={cyan}{red!80!black}]
  (baa) to[out=-80,in=150] (bbb);
\end{tikzpicture}
\end{document}

Answer 1

The tikz code is faulty. It uses \global\setlength. This relies on a side effect which breaks if the calc package is loaded. If you use \global\mylen instead it works:

\documentclass{article}
\usepackage[
a4paper,
margin=30mm
]{geometry}
\usepackage{amsmath, amssymb, amsthm}
\usepackage{tikz}
%
\usepackage{etoolbox}
\usepackage{mathtools}
\usetikzlibrary{graphs}
\usetikzlibrary{positioning}
\usetikzlibrary{intersections}
\usetikzlibrary{decorations.markings}
\newlength\mylen
\tikzset{
    bicolor/.style n args={2}{
        decoration={
            markings,
            mark=at position 0.5 with {
                \node[draw=none,inner sep=0pt,fill=none,text width=0pt,minimum size=0pt] {\global\mylen\pgfdecoratedpathlength};
            },
        },
        draw=#1,
        dash pattern=on 0.5\mylen off 0.5\mylen,
        preaction={decorate},
        postaction={
            draw=#2,
            dash pattern=on 0.5\mylen off 0.5\mylen,dash phase=0.5\mylen
        },
    }
}
\begin{document}
\begin{tikzpicture}
\node (bbb) at (0,0) {bbb};
\node (baa) at (150:3) {baa};
\tracingmacros=1
\draw[->, bicolor={cyan}{red!80!black}]
  (baa) to[out=-80,in=150] (bbb);
\end{tikzpicture}
\end{document}