Are you talking about the "E" at the end of a Colt's serial number?
If so, this is my meager experiance:
I own a Colt Combat Elite, "Enhanced" model, that I purchased in 1994.
It is basically a poor man's Gold Cup. It has the target sights, better parts, better fit, nice factory trigger, etc. It reminds me of my friend's "pin" gun.
I have seen other Combat Elites and they looked more like the 1991A1 with a blued slide over a stainless frame. The parts weren't as nice and the fit was so-so. I spent $1000 for it and it shoots better than I can.
The Enhanced Models were introduced during the 90s, which featured lowered and flared ejection ports, beveled mag wells, relief cut under the trigger guard, and Colt's version of a beaver tail grip safety. These were series 80 pistols with the incorporated passive firing pin safeties.
I have a goverment model enhanced.Ibought it in 1994,it has the features that DoubleaAction said.I love this gun ,is very nice to shoot with it.Im found that is very reliable and sometimes I crry it for my defense.