Google Message Security for Google Apps Administration Guide - Manual (Page 146)

146 Message Security for Google Apps Administration Guide
Message Center Color Palette
Use the Message Center Color Palette to set Message Center colors for your
users. This setting also acts as a default for all sub-orgs.
To set your Message Color Palette
1. In the Administration Console, go to the Orgs & Users tab and select the
organization which contains your users.
2. Click the Branding link.