Edited Issue: DataGridCheckBox blue background [20210]

I've noticed that a datagrid cell with a checkbox being edited exhibited a blue background; See screenshot and wonder why it is so...

I noticed this piece of code in DataGridCheckBox's OnApplyTemplate override:

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

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

```

This really seems like test code to me... Would you mind removing it?