I tried all of the other approaches, and the best case was the correct background being painted, but the group box line was visible behind the group box label. A group box is really a button ( with a static label on it ), and so the button needs to paint the text background solid to draw over the group box line.
This solution creates a brush out of the background of the parent. So, this even works if the tab/dialog background is a drawn image.
The function below can be used for any control, but is only needed in this case for statics and group boxes.
Note that the CBrush (m_brush) is a member of the parent ( dialog )