Make the $, equation and align math environments globally blue

Question

I'd like to make all my math blue. So far I only use the $, equation and align environment, so it'd we nice it it worked for those. If it works for others, that'd be even greater.

\documentclass{article}
\usepackage{amsmath}
\usepackage{xcolor}

\everymath{\color{blue}}
\everydisplay{\color{blue}}

\begin{document}
    Let $\vec{v}$ be some vector. A fancy one.

    \begin{align}
        \vec{v} = \vec{a} \\
                &= + \vec{b}
    \end{align}

    \begin{equation}
        \vec{v} = \vec{a} + \vec{b}
    \end{equation}
\end{document}

I get

untitled.tex|14 error| Improper \halign inside $$'s

I know I could just write my own environments but I really would love to just tell it: Make everything blue no matter what.

Answer 1

\documentclass{article}
\usepackage{amsmath}
\usepackage{xcolor}

\everymath{\color{blue}}


\AtBeginEnvironment{equation}{\color{blue}}
\makeatletter
\def\maketag@@@#1{\hbox{\m@th\normalfont\color{blue}#1}}
\makeatother

\begin{document}
    Let $\vec{v}$ be some vector. A fancy one.

    \begin{align}
        \vec{v} = \vec{a} \\
                &= + \vec{b}
    \end{align}

    \begin{equation}
        \vec{v} = \vec{a} + \vec{b}
    \end{equation}
\end{document}

Answer 2

If you use either XeLaTeX or LuaLaTeX to compile your document, you may render all inline math and display math material in blue automatically by employing the unicode-math package and setting the option Color=0000FF while executing \setmathfont. E.g.,

\usepackage{unicode-math}
\setmathfont[Color=0000FF]{Latin Modern Math} % set a suitable math font

Here's an MWE (minimum working example) and its output:

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{Latin Modern Math}[Color=0000FF]
\begin{document}
Let $\vec{a}$, $\vec{b}$, and $\vec{v}$ denote vectors. Suppose
\begin{equation}\label{eq:new}
     \vec{v} = \vec{a} + \vec{b}
\end{equation} 
\end{document}