The fact is that different models of the same weapon have the same color, making it:

a) Impossible to distinguish
b) Implying that it is the same model as the lesser ones

I think that the weapons fire for the higher models, i.e., Neutron Blaster MKIII > Neutron Blaster MKI, should be darker, implying that it is more concentrated and does more damage, like it does in reality.

For example, an AAP should be darker than a regular Positron Blaster.

I'm not sure about darker per se, but some sort of difference is necessary. If you recall, all flares used to share explosions until the graphics guy did his magic on them. The same needs to be done with the blasters and I'm sure it will in time.

Yeah, I think what idd means is to up the saturation, not "make it darker".

But yeah, +1 to minor color variations between weapons of the same class.