What is the importance of Greta Garbo as noted in the nonfiction book, White?

Greta Garbo is only mentioned a handful of times in the book, but she serves as an example of a white, idealized female figure in Hollywood movies. The way she is lit compared to her co-star John Gilbert in "Flesh and the Devil" shows that she is purer than he is, for she is lit so brightly as to be almost translucent, while his figure carries with him a certain shadowy, poorly-lit quality implying dark desire for a transcendent female idol. Dyer uses a striking photograph of Greta Garbo in the book to illustrate lighting techniques in Hollywood.