Actually, the girth belts are the same, but the color and connection methods are different. In all cases the girth belt is a white/natural mohair horse girth with a diagonal weave. However, the pre-prod/ESB Fett is Dark Brown while ROTJ Fett is Dark Red.
Additonaly, the jury is still out on how the belt was connected in the back. Most agree that two 1" wide black straps were used to connect the four buckles on the girth. The straps were sewn to the buckels on one end, and buckled (like a regular belt) on the other end. The question is what material was used? Was it nylon (like in the MOM and ASW displays), was it leather (some think leather is screen accurate), or was it an elastic strap?
Here is the thread with the above information and detailed steps on how to die a girth:
http://tdh.prop-planet.com/viewtopic.php?topic=1408&forum=3
In general, if you have to ask if there is a difference, there usually is.

Differences between the movies, differences between sceens in the movies and differences between the various tour displays, pre-pro photos, and Special Eddtions. Very frustrating ... I know, but pick one you like and run with it, or mix and match. It's totally up to you.
BTW, the search engine can be your friend.
Gator