Harmy said:

they show you the shot from inside the cockpit of Luke's speeder flying under the AT-AT from the original version and point out how it's transparent and then go on to talk about how they recomped all those shots in a computer and "eliminated all the transparency" and then they show you the same shot from the SE, which is darker and bluer but just as transparent as the original.

I must say, having just watched the GOUT version of Empire, that you can't really see the transparency (unless you really really look for it) in the unaltered version of the shot anyway.