Change indicator color from white-black to white-transparent

Change indicator color from `white-black` to `white-transparent` just so that it looks less odd against a colored background. :star2: 

Before

![image](https://cloud.githubusercontent.com/assets/1153134/4021483/79c6b518-2af5-11e4-8a5b-d4880fa0c8c4.png)

After

![image](https://cloud.githubusercontent.com/assets/1153134/4021484/7fb8c95c-2af5-11e4-82e8-e3cb08f2b173.png)

Against a black background it'd be the same:

![image](https://cloud.githubusercontent.com/assets/1153134/4021493/d3b1aeac-2af5-11e4-9862-e504c132e174.png)