Today's fun Internet Explorer feature (7 and 8 both): there's an accessibility option which lets you override website colours, so that for example, everything becomes green on black. Great, right? Except, it doesn't work properly in our forums. All the forum posts have a white background.
Turns out that in Internet Explorer, if you specify a background image for something while leaving the background colour transparent, it always draws it with a white background when in this accessibility mode.
To put that another way, the fix I made to get rid of this unwanted white background? I set the background colour to be white. Yes, really.