^Just a few little random colour botches were fixed, like Kirk momentarily wearing a red shirt for a few seconds in an episode (which, oddly, is shown in one of the menu pics). I think the Klingon outfits were changed from pink to purple as well.
I may be wrong since I saw TAS long ago before getting the DVD, but I think they toned down the orange of Kirk's hair and gave him a natural skin tone as well. I think he was white as a sheet in the originals (but it was *years* ago so I may be misremembering)
The Delta Triangle change annoyed me, because it was so pointless. What they should have done and didn't was change the Andorian's skin in "Yesteryear" blue.