Adjusts image color to match text color.

Fixes #211

Before:
![screen shot 2013-11-13 at 10 54 24 am](https://f.cloud.github.com/assets/1435271/1533459/e12a9aac-4c85-11e3-8220-5c4702c6f701.png)

After:
![screen shot 2013-11-13 at 11 00 38 am](https://f.cloud.github.com/assets/1435271/1533463/e8d8c7a6-4c85-11e3-9aa6-80aced70265a.png)