Update background message color to match theme

This: 
![image](https://cloud.githubusercontent.com/assets/82437/2611536/e162c96e-bba6-11e3-8ba4-6cbd5ce8380a.png)

Instead of this:
![image](https://cloud.githubusercontent.com/assets/82437/2611540/0781b51a-bba7-11e3-8b30-10ed6c992fdf.png)