R1:2dcfcb001192

Fix embed icon colors in Pholio.

Summary: Fixes T3598. Swapped the colors to white.

Test Plan: review embedded mock in task

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T3598

Differential Revision: https://secure.phabricator.com/D6506