Please, imagine the rocket launcher like RPG, where the grenade holds outside of launcher. Or the plasma weapons with lighting that depends on type of clips.
Have you considered this system would be totally dependent on color? And that color blindness, in one form or the other, affects about 10% of the world population?
Or that there's 8 vanilla damage types, so you'd need at least 7 different colors (for Melee it wouldn't be needed) but the palettes are limited in choice? And if you use some colors like yellow, green, brown, etc., the lightning will be barely discernible when superimposed against the terrain?
Imagine that when you hover the cursor over the weapon, it displays both the damage type and the damage power. To me that would be a lot more useful than a lot of flashy graphic effects that won't be that easy to distinguish and that will be there just for the firework show. But this is only my opinion.