There is a word meaning "To Make Purple". To my knowledge it's the only defined word of its type. I have been made aware of another word (thanks, Oolong) meaning "To Make Brown". This brings the total up to two!

The first word is impurple or empurple and is without a doubt one of the coolest words I have ever seen. Haven't you ever wanted to impurple someone or something? Have you ever empurpled an object without realizing you had? Join the club.

The second is imbrown or embrown and though, in my opinion, it lacks the royal class of impurple, I now acknowledge its existence :).