Set background colors.

Summary: Set background colors similar to the background images so slow page loads look nicer.

Test Plan: Reload page.

Reviewers: epriestley, btrahan, codeblock

Reviewed By: codeblock

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4459
Merge branch 'master' of github.com:facebook/phabricator

Conflicts:
	src/__celerity_resource_map__.php