There is a very subtle colour variation between the background of the panel and the background of the player control, but i cannot find the issue in the skin. In the skin file it appears that they are both set to 40,40,40. I maybe looking in the wrong place though.
<element id="PlayerSidebar.Background" bg="40,40,40" fg="225,225,225" bdr="40,40,40" />
<element id="ApplicationBackColour" bg="40,40,40" />

Any help would be appreciated