add variable color

before:
![before](https://f.cloud.github.com/assets/29762/2394493/cfe3101c-a9b4-11e3-9266-423def33df51.png)

after:
![after](https://f.cloud.github.com/assets/29762/2394495/d37c63b8-a9b4-11e3-93c9-595f4f9f3424.png)