Google has released theme feature for it’s Gmail application that enable users to change appearence or look and feel for it’s mail interface. This feature can be accessed under Gmail settings on Theme tabs.
However, for mail application hosted in Google Apps, this feature is not enabled by default. After doing a bit searching, i found a solution that worked on my mail application.
To enable theme feature:
- Login into your Google Apps control panel.
- Go to Domain Settings menu.
- Under New Services and Pre-release Features option, check the two available check boxes.
- Click Save Changes button.
Note:
Sometimes it takes time for the changes to be applied, so just wait for it… 🙂
by 
“New Services and Pre-release Features option”
Where is that?
Manage this Domain->Domain Setting->Email->Themes ( Please tick “Let users choose their own themes.”)