Some updates

1. Fix a bug, when run in windows with mono, `TextArea.BackgroundColor` could't take effect.
2. Add new property `TextColor` to `TextArea`(Mac's TextColor not test).

![2](https://cloud.githubusercontent.com/assets/7532281/4055726/63d99fea-2dac-11e4-93c4-83c3ab487bb0.png)
Could this be removed from the pull request?