Despite the time in which they were written, the Oz books are relatively free from cringe-worthy racial stereotypes. Well, except for The Woggle-Bug Book, but that doesn't really count, does it? One exception is in The Patchwork Girl of Oz, which introduces the Tottenhots, a wild and mischievous black tribe that lives on the plains near the Winkie-Quadling border. The name is obviously a play on "Hottentot," which is what European settlers originally called the Khoikhoi people  of southwestern Africa. The book describes them as follows: "Their skins were dusky and their hair stood straight up, like wires, and was brilliant scarlet in color. Their bodies were bare except for skins fastened around their waists and they wore bracelets on their ankles and wrists, and necklaces, and great pendant earrings." They live in houses that look like overturned kettles, with cushioned floors, and are nocturnal. I can't say I ever found their portrayal offensive, but then I'm a white guy. When Books of Wonder published an edition of Patchwork Girl, they left out some of the descriptors and one of the illustrations of a Tottenhot. There is an additional dose of offensiveness in Rinkitink, with a Tottenhot being described as "a lower form of a man," and apparently less human than a Mifket (described in John Dough and the Cherub as being sort of halfway between human and animal). When Books of Wonder published this one, they didn't alter any of the text, but they removed an illustration.
The post-Baum books contain some stereotypical portrayals of different ethnic groups, and Neill's drawings were often worse than the descriptions. Royal Book has the pseudo-Asian Silver Island, and other books bring in Arabian-style countries. I've already discussed the black slave revolt in Silver Princess; and Wonder City says that the Emerald City fire department is made up of "Fire Injuns," depicted as Indian heads on wheels. Most of these seem pretty harmless to me, but they're definitely embarrassments when I describe the books to others.
 As with many tribes, "khoi" apparently just means "people." So my phrasing would literally translate to "people people people."