add color for indent guide

Before
![screen shot 2014-03-16 at 10 20 34 pm](https://f.cloud.github.com/assets/596262/2431061/176cc8a4-ad18-11e3-97ca-3b7cd8f7e123.png)

After
![screen shot 2014-03-16 at 10 23 26 pm](https://f.cloud.github.com/assets/596262/2431060/176c42a8-ad18-11e3-904d-b79a35a14741.png)