use git-gutter+ to replace git-gutter.
init git-gutter+ package.
add mu and mu-cite two packages for mu4e.
disable git-gutter+.
switch back to git-gutter again. Because it show git diff signs instantly.

Because of the window-change-configuration-hook.
set git-gutter unchanged sign to `nil` to solve unchanged sign color problem.
disable to load git-gutter+ package at Emacs initial.