dim "Use arrow keys"

This is not the same as the previous`gray` and works with any theme as it only reduces the opacity.

![screen shot 2014-08-15 at 18 24 31](https://cloud.githubusercontent.com/assets/170270/3935722/f9c82610-2498-11e4-9dd0-dd92909bd436.png)
![screen shot 2014-08-15 at 18 23 12](https://cloud.githubusercontent.com/assets/170270/3935723/f9dced52-2498-11e4-906c-4421366e3976.png)