one was the military intentionally gave black soldiers a dishonorable discharge, as a way to make them ineligible. another was they had them courtmartialed for phantom offenses. others were just outright denied
even if they could partake in GI Bill, other racist practices such as redlining and school segregation diluted the benefits..
https://en.wikipedia.org/wiki/African_Americans_and_the_G.I._Bill