Better dark-theme support in Luna+

Using java color constants that support dark-theme in Luna+.  Here are screenshots of default and dark themes for Luna using Ubuntu 14.04.

![screenshot from 2014-07-18 00 04 53](https://cloud.githubusercontent.com/assets/595221/3616047/b30ff2ce-0dce-11e4-98ce-4893108dcbb1.png)
![screenshot from 2014-07-18 00 05 08](https://cloud.githubusercontent.com/assets/595221/3616048/b32d8d98-0dce-11e4-97d0-506e15aabbd2.png)