[Redesign] Pop color up on header status tags

Summary: Ref T8099, Move these to alpha channels so different header colors pop the color up equally.

Test Plan: Test Documents, Maniphest, Workboards

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8099

Differential Revision: https://secure.phabricator.com/D13440