JonB, thank you very much! That worked. I had tried to write some code that iterated over Obective C UI items, trying to find the item that mattered and changing it's color, but I never got it to work.
Eventually, I'll try to figure out the hierarchy using your code as a guide, and match to the right names so that the code is somewhat more robust to version changes. For now, I added the following method to my ui.View-derived class, that allows me to change the title bar color dynamically.
def change_title_bar_color(self, hex_color):
""" Change the title bar color to the passed color.
vv = ObjCInstance(self)
bar_bckgnd = vv.superview().superview().superview().subviews().subviews()
bar_bckgnd.backgroundColor = UIColor.colorWithHexString_(hex_color)