答案1
以下是两种自己提出的可能性(从评论转换为答案),其中冒号点与等号的高度相匹配:
\documentclass{article}
\usepackage{fourier}
\usepackage{stackengine}
% THE FOLLOWING WORKS WHEN fourier PACKAGE IS NOT USED
\newcommand\newvcentcolon{\abovebaseline[.07ex]{\stackanchor[.18ex]{.}{.}}}
%\newcommand\newvcentcolon{\abovebaseline[.02ex]{\stackanchor[.19ex]{.}{.}}}
\newcommand\colonequalA{\mathrel{\newvcentcolon{=}}}
\usepackage{scalerel}
% THE FOLLOWING WORKS WHEN fourier PACKAGE IS NOT USED
%\newcommand\colonequalB{\mathrel{\hstretch{.085}{=}\hspace{.2ex}{=}}}
\newcommand\colonequalB{\mathrel{\hstretch{.13}{=}\hspace{.2ex}{=}}}
\begin{document}
\(x\colonequalA x+1\)
\(x \colonequalB x+1 \)
\end{document}