Greyed out some icons, removed colors from Phriction updates

Summary:
@chad The colors were indeed terrible. Why didn't you tell me

Also greyed out diff icons when no diff available. Makes it more clear that you can't click it on mobile.

Test Plan: Saw it on mobile and desktop.

Reviewers: epriestley, chad

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5694