No matter what the background color of my group node is, the "expand" section (where you click the little cross to expand the sub-nodes) always has a white background color. I'm not talking about the little expand/collapse box itself, I'm talking about the whole "section" behind it.

It looks particularly bad if you add checkboxes.

I can't seem to find a way of changing it, can somebody help? It would be much appreciated!

I've added a screenshot to illustrate the problem.