How does Myrtle, Tom’s girlfriend, compare with Daisy, Tom’s wife?

The first, obvious difference is in their physical appearances. Daisy is light skinned and blond, while Myrtle has a more swarthy complexion and dark hair. Daisy dresses mostly in white, which represents her cleanliness and purity, while Myrtle chooses vibrant colors that reflect her loud personality. Myrtle's bright colors exacerbate the contrast between the "all white" world of the upper class and world she is so desperately trying to crawl out of. Daisy is ethereal and graceful, while Myrtle is robust and brassy. A slight wind could probably knock Daisy off of her feet, while Myrtle would probably stand strong in a hurricane.

Although the physical differences are relevant, it's the differences in upbringing/class and personality that make these classic foils interesting. Daisy has been raised in privilege, while Myrtle has had to claw and scratch for everything she has. Daisy considers her wealth her "due", while Myrtle's increase in status (through Tom) is fairly recent. Daisy is "old money," and therefore comes from "good breeding." Myrtle, much like Gatsby, is considered an upstart with no business hanging around with New York's elite. People with "class" shouldn't (gasp) EARN their money. People of class either inherit their cash or marry into it. When Myrtle is killed by Daisy in the hit and run accident, this shows that, no matter what, breeding will always win out.