How do i set the color of the Ribbon Background to be single color (not a gradient)

It seems like there is no way to have the ribbon's color to just be a single color.
If i set

BackgroundColor = new SolidColorBrush(Colors.Red);

it looks like it is dark red at the bottom, and lighter red higher up in the Ribbon.
I want it to just be the single color. What can i do to get this? I've also tried setting Effects = null,... Any ideas?