Xanthin, without the second 'a', is a yellow colouring matter from the plant, madder and its adjective is xanthic. XanthiAn means related to Xanthos, the capital of Lycia in ancient times. Xaverior is not recorded in either Chambers or The Oxford English Dictionary, though it may possibly be an Americanism. In British terms, therefore, it would appear that xanthin is the only x-colour.