from Xanadu, the English form of Shangdu, Kublai Khan's summer capital; reference sites disagree on whether the color was named for the place, Coleridge's poem 'Kubla Khan', or the Xanadu philodendron
Fun Fact
Xanadu is one of the very few English color names that begin with X, which is why it shows up on nearly every list of colors starting with that letter.