In answer to the original posters question:

From a certain point of view (god, I can never use that expression and be treated seriously) the 1995 THX set might be percieved as altered--its color timing. Even though every release looked a bit different because each release is individually color-timed, the 1995 release seemd to point to deliberate artistic changes which would later be confirmed in the SE. For instance, the scene where R2 gets zapped in the canyon was originally fairly brightly exposed, but on the THX it is dim, much darker than any telecine prior, as if it is much later in the day--on the SE, it would be digitally re-timed to be sunset. Another example is Hoth--though it may be argued that this was not the first release to introduce blue emphasis on Hoth, the intensity here far outwieghs everything that came before it; as originally photographed Hoth is fairly neutral looking, but here the scenes all have a heavy blue shift to them. In the SE this would be emphasized more and in the 2004 SE pushed to the extreme.