Created Unassigned: DataGridCheckBox again has blue background [22312]

A previously fixed bug is now broken again. The previous bug is item number 20210.

[DataGridCheckBox blue background](http://wpftoolkit.codeplex.com/workitem/20210)

From the code of the CheckBox.cs the blue background is back in the latest version.

```
public override void OnApplyTemplate()
{
base.OnApplyTemplate();

ChildCheckBox.Background = new System.Windows.Media.SolidColorBrush( System.Windows.Media.Colors.Blue );
}
```

Please remove the line which sets the background to Blue.

Thanks