R1:6b7487335823

Update icon color in Durable Column header-text

Summary: Moving to an rgba color here to work better with all the various header colors.

Test Plan: Reload sandbox, see new icon color.

Reviewers: epriestley, btrahan

Reviewed By: btrahan

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D12176