If you don't want your diff so fancy (pun intended, and I'm sorry) but you still want the inline highlights, the script comes with git (https://github.com/git/git/tree/master/contrib/diff-highligh...):

    ln -sf "$(brew --prefix)/share/git-core/contrib/diff-highlight/diff-highlight" ~/bin/diff-highlight

and add to .gitconfig

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