The Black actors who want to become white sit in what looks like a dentist chair invented by Dr. Junius Crookman (played by Tariq Trotter, from The Roots, who is also the lyricist, and one of the composers). After they're "tranformed," they don't appear white in any way, and apart from the lead character (Brandon Victor Dixon as Max Disher), they return to being members of the chorus/company. But the story follows Dixon, who "acts white," which is to say, his physicality and body language changes, and behaves more like the other white characters in the show. Although it may sound confusing, it isn't. It's all very cleary conveyed.