Topps, I think was a black colour. After he turned to his current colour, he remained that way throughout the sequels. I guess to show continuity, but it really doesn't make up for the cheap way they were done.
Littlefoot is the main character which shows the most colour contrasts. He is brown, blue, green, and I believe lavender at one point. It basically means his mood swings. After the original, the new director didn't care about that all.