Due to the manner of liches being literal embodiments of magic and thus not having a physical form, technically Barry is the lich and possessing an otherwise empty body that just happens to be genetically his in this specific instance. And the shape his lich form takes is a red robe. So if he doesn't possess his body, the physical form will be nothing. unless the form is another person with their own opinion of Altair

But yes, white definitely works!