ComboBox colors

[Joaquim Schmidlap <schmidlap schmidlap org>]

OK, I've been trying to change the background color of a Gtk::ComboBox and
can't figure it out.

I've tried modify_bg, modify_base, and set_style, and it's still the same
default gray.

What's the trick?

(BTW, ultimately, I'll want to change the color of the arrow and the popup
elements, too...I assume the same approach will apply? Or is there something
different I'll need to do to access the different internal bits?)