Art source: https://www.deviantart.com/angelcondom/art/Saruman-of-many-colours-147889671
Book quote, Fellowship Book II, Chapter 2:
"The Nine have come forth again," I answered. "They have crossed the River. So Radagast said to me."
"Radagast the Brown!" laughed Saruman, and he no longer concealed his scorn. "Radagast the Bird-tamer! Radagast the Simple! Radagast the Fool! Yet he had just the wit to play the part that I set him. For you have come, and that was all the purpose of my message. And here you will stay, Gandalf the Grey, and rest from journeys. For I am Saruman the Wise, Saruman Ring-maker, Saruman of Many Colours!"
I looked then and saw that his robes, which had seemed white, were not so, but were woven of all colours. and if he moved they shimmered and changed hue so that the eye was bewildered.
"I liked white better," I said.
“Check the fit, Gandalf—dare you step to this!?”