While we're at it, don't forget "Coltalloy" for the early Colt Commanders (aluminum) and "Coltwood" for most of the grips (plastic).

With that said, if you marketed a gun as "plastic-framed", I doubt you'd have as many customers. On the other hand, I honestly don't think calling a gun "aluminum-framed" would be a negative. With that said, when the Colt Commander was introduced, people were used to aluminum bending. Even though the Army never accepted the Commander, they did at least acknowledge its structural integrity, and my guess is that's why you saw Colt marketing its guns as "Coltalloy" and then just plain "alloy". But aluminum has aged well enough that you can call gun "aluminum-framed" without dissing it (especially since the actual metallurgy got better).

"Plastic" doesn't have particularly high connotations, though. "Plastic gun" and "plastic frame" have evolved into derisions and unlike "aluminum frame", I don't think that will change any time soon. Still, I do see another case for specifying the kind of plastic. Thermoset, Polymer, ABS, and even Bakelite are or were all used in the gun industry and all are pretty different from each other. If you're going to call a plastic gun a "plastic gun", you might as well also call any gun made of metal a "metal gun".