I have no idea where that color is being pulled from, but the skins I have that do not have the jumplist skinned are using a color from somewhere.
Depending on the skin, you may be able to get away with using another image from it in that place. Maybe the normal pop up menu background would work there, or possibly you could wip up an image for it, even if it's just a solid color panel.
...or ou could ask the original author to make you one.