Actually, I have just figured it all out.
Anakin polishes off Mace because all along he was angry about only one thing. Mace's special purple sabre. He orginally wanted one, but Obi-Wan made him take the blue one. This explains "Obi-Wan is holding me back!" from Attack of the Clones. He really wants to kill Obi-Wan because he reveals his darkest secret: his dreams were not about Padme's death, but about Mace's. After Mace dies in Anakins dream, they find out Mace left the purple sabre to Obi-Wan in his will. When he shows up with the purple sabre, Obi Wan knows that Anakin is evil because he must have killed Mace! Obi-Wan tries to tell Anakin that his dream was wrong, the Sabre was to go to Mace's son, but Anakin will not listen!
Episode IV is remastered to reflect the fact that the lightsabre does make it to it's rightful owner. Luke's "A New Hope" blade will be made purple.
Anyway, Purple is kinda like Red and kinda like Blue, so what we get is Blue vs. Red and Blue.
Everyone is happy!
Carnage