Tweak alert states in header a bit more

Summary: The sky blue colors in the alerts was problematic in other color headers (not black). Rather than hand tweak each color, just going with white seems best. There is also a small animation now, which you may or may not like. It is playful and enjoyable to me at least.

Test Plan: Tested various header colors with and without alert notifications.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11838