It's not so much the UV that's your problem. Is this the side/back or is it your the front that you would view through? A solid background would probably be your best bet.
On the other hand, I'm still not convinced that light through the window is a significant cause of algae. If everything else is balanced, it shouldn't matter (with the exception of Seaman's comment about the light cycle). How well do the timing of the morining light and your light's on time coincide? If they were about the same, you shouldn't have any problem. In fact, I'd be tempted to set my timer to turn lights on just after the full sun was coming through the window, give the tank a real sunrise effect!