Based on info i've pieced together myself and from others, all years of mystique tails have the clear lenses underneath.
You don't sand the red lense off, it needs to be cut off. I suppose you could "chip" it away, but cutting it is more controllable.
Making them clear is fairly simple, although you still need to be careful.
Getting the lights to still put out red light is more involved. I chose to retrofit round LED truck tail light modules.
Some other links:
http://www.contour.org/ubbthreads/showthreaded.php?Cat=&Board=aesthetics&Number=926886&page=&view=&sb=5&o=&vc=1
http://smg.photobucket.com/albums/1003/amarv12/Clear%20tail%20project/
Like the other guys said searching for phrases like "clear tail" or "LED tails" will give more info.
