Lighten up red and green in diffs
Summary: Because new+old stack, these colors were darker than intended. Lightening them up a little bit.
Test Plan: Review a diff with new + old code and addtion subtractions.
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D15994