Not Rick had a great answer, but I wanted to try to contribute simple examples:
True, skin color is a trait that can be traced by DNA, but so is eye color, or hair color. We could easily create “races” based on “Brown hair vs blonde hair”, “brown eyes vs green eyes”, “people who need glasses vs people that don’t”, “shorties and tall-os”, “those who can roll their tongue, and the inferior swine that were never blessed by the Great tongue father.”
All traceable in the same way as skin color, but we consider them “features”, and not race defining traits.