Native American is really the only race/ethnicity category that may require some verifying documentation (tribal enrollment). Everything else is basically on the honor system, since colleges do not want to get into the business of determining race classification (for Native American, they outsource it to the tribes). For example, someone who may appear white may honestly identify as (also) black on a regular basis (e.g. http://theundefeated.com/features/isaiah-hartenstein-nba-draft-2017/ ), but someone else who may appear white may only identify as black on a college application based on 1% African ancestry in a DNA test. A college may reasonably want to stay far away from the often subjective guesswork of determining which is actually the case.