Remove contextual +/- in favour of colour highlights? As a person with red-green colourblindness all I can say is: Lol. Nope.
From the git book itself: `git config --global color.diff.meta "blue black bold"`
(In Emacs, if you're using git, magit is an amazing package. You can select a commit from the logs, dive into the diff for a file caused by that commit, highlight a region of the diff and revert the change in your working copy. It's wonderful.)