Actually, if you really want to be technical, there's 6 versions of Boba Fett.
McQuarrie Concept (All White Version)
Pre-Production ("mustard and ketchup" Gauntlets, Mulit-colored JP)
SW Holiday Special (Blue and Yellow)
ESB (Green Gauntlets and JP, helmet has a slightly different color paint scheme - EE-3 looks different - silver barrel & sidearm on right thigh/buttock)
ROTJ (Red Gauntlets, Multi-color JP, Helmet paint scheme, no sidearm, different EE-3)
and Special Edition - ESB Helmet with ROTJ Suit (could be the other way around, if it is, please correct me someone!)
I believe these are the very basic differences, but I am sure the many fine people here will be willing to give you a more in depth idea of what is what.