Has anybody tried high temp coloured heat shrink on their plug wires?

 

Why? For decoration?

Might make the wires stiff for routing. The wires don't come near hot parts. Unsure why you'd do this.

 

For the same reason people buy blue, red , yellow or black. Might want to colour match to the car etc. I bought blue ones for my dark blue car and they weren't cheap. $30 of heat shrink and your engine bay has a new look that you can peel off later if you want.