Changed the color of the Close button in the Clean style.

Small change: The color of the close button when it is pressed is now red.

Before, when you pressed the close button, it would appear as a greenish-blue color. Now, it is a pale-ish red color, similar to GitHub for Windows.

![cb](https://f.cloud.github.com/assets/251501/1730108/b7ef0308-62d3-11e3-9450-58bd0df64a4a.PNG)