Change backgroud color with color gradients
===

I want to change the background color from my combobox.
But I would like to retain the color gradients.

![enter image description here][1]


I've tried using this code but still does not get the effect.

    <Setter Property="Background" Value="White"/> <!-- It's only white :( -->
How can I solve this problem?

  [1]: http://i.stack.imgur.com/pKkvH.png