I didn't notice this in Empire at first but where I first saw it was in TPM was when they are leaving Tatooine, Darth Maul attacks Qui-Gon and I swear all during that fight Darth Maul's saber is like and orangey yellow color. And I believe I saw it in Empire too because all during that fight Vader's saber would go from different shades of pink to the normal red. But I believe the name color change like with Maul's happens during the part when he knocks Luke down and Vader jumps down and it looked exactly like how Mauls's saber color did. Now I don't believe it's my eyes playing tricks on me and wanted to see if anyone else noticed it and to see if I was the first to notice this.