R1:96fbf37dcc11

Bring up contrast on light green / red diffs

Summary: Minor color saturation here, ideal for low quality monitors.

Test Plan:
Review new colors in various scenarios.

{F2305178}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17141