Lightens the background color of detail messages

Before:
![screen shot 2014-12-12 at 9 07 18 pm](https://cloud.githubusercontent.com/assets/186715/5422647/06f7e67e-8243-11e4-9941-cabae25648f9.png)

After:
![screen shot 2014-12-12 at 9 06 38 pm](https://cloud.githubusercontent.com/assets/186715/5422648/0bd90420-8243-11e4-8600-a8d5ff495a66.png)