So here's my thinking, shock and lightning shine white and blue, most warpy effects are purplish, fire ranges from shades of red, orange and yellow. Then there are weird skills with a color that shouldnt be, like shockwave which is white-yellow being a warp thing. Then there's mixing stuff so you end up like a rainbow of death going around with black smoke steps, purple dashes, a red circle, orange explosions, blue shocks and whatever it is the skill you spam. 

Why be a walking rainbow when you can have your own color/element, or even on the contrary, why be a haphazard rainbow when you can be a proper one? For example, all purple or red lightning, or blue fire or purple fire, or red poison effect to make it look bloody, maybe all white or yellow white to feel holy or sacred, maybe green fire to make it look nurgly, etc.

Honestly this kind of customization isn't necessary but it is a neat thing to have, customization is always nice, moreso when its just for cosmetics. Then again anyone can do it by finding the right DSS file and editing them manually, but before spending hours and hours trying to discover which one belongs to which skill (and there are a lot of them) i'd like to suggest the devs to make a function ingame like the one to change the appearance of the visible equipment.

If nothing happens, as it was proven for years of waiting for things to happen, i'll still most likely do it myself cause that's how much i want it, but i'd rather the devs do it properly than me basically modding the game. That was my grain of sand. Cheers.