Remember that if you have ANY IE8 copies open in taskmanager then the colour change will not be picked up until those have been closed.
I'm having trouble with that too now. I didnt have IE8 open at all and I cant seem to change it.
When it changed before the update, I was toying with the button face and button light and button shadow...all three seemed to change the color, now it seems that none of them do.
Am I doing something wrong? Is there a setting somewhere that is overriding my color changes? I dunno. Help me Obi Wan!