The original MX were black, and were made between 85 and sometime in the early 90s from what I can tell. The originals have a lighter spring, and the stem is possibly made of a different plastic formula, and also the legs that hit the crosspoint have a tiny bit less angle on them. The larger logo is the easiest way to spot them, but there may be some of the smaller logo with the orignal internals as well made during transition period. Some earlier blues can be spotted this way as well with the large logo, but the most imortant part there is the 2nd piece of the stem is made out of the same black plastic as the original blacks. Whatever the case with the older black plastic, is it has much less friction than later variants resulting in much smoothe action. I like to describe it as buttery.
Vintage browns only feel better because they have turned into reds after having thier little tactile point worn off.
