Given how easy it is to prism light, you'd have to go out of your way for your lightsaber NOT to be rainbow!
Or you could head to Quora: https://www.quora.com/Is-there-a-ra...s-with-all-the-colors-in-the-visible-spectrum Seems possible:
The question now is, why wouldn't you have one of these just to leave folk guessing as to your allegiance? "He's Sith! Wait, neutral! Wait, Jedi Guardian! No, Consular! No... Now he's Samuel L. Jackson?!"
Isn't it cute how @Bill Carson thinks his mom is nice. His spelling got better this year too. He might even graduate from first grade this time.