I agree with Matty. Certain spells have specific particle effects to make them recognizable, especially when it comes to dueling - you're meant to be able to identify specific spells by their visuals. The only spells (that I can think of) that change in colour based on your wand effects are Flipelius, Appareo, Ascendo, Finite Enchantum and Obscurio. Appareo and Ascendo both are fine since you can see the player teleporting and moving around. Flipelius and Obscurio are low level spells which aren't used much after you get more spells and Finite has a specific animation with a mix of another colour.
Tl;dr, would be cool but maybe too confusing for dueling.