MahApps/MahApps.Metro — pull request #1713 by mgnslndh (2014-12-18 15:09:19+00:00)
Title: Fixed background of ComboBox

The `ComboBox` styled used a gray brush as background instead of the
control background brush as `TextBox` do.

This was not an issue when using the default themes. When creating a new theme where the background is dark blue this became an issue since the background of a `ComboBox` was gray and not dark blue.

This is my first contribution on GitHub ever, so I decided to do something simple.