diff-highlight

$ mkdir ~/bin
$ cd ~/bin
$ curl https://raw.githubusercontent.com/git/git/master/contrib/diff-highlight/diff-highlight -o diff-highlight
$ chmod +x diff-highlight

PATH通す~/.zshrcなどに追記

PATH=$PATH:/Users/<USER名>/bin

~/.gitconfig

[pager]
log = diff-highlight | less
show = diff-highlight | less
diff = diff-highlight | less