Most of the black units in WW2 were support... truck drivers, longshoremen, etc. Notable exceptions like the Tuskegee Airmen existed, an some 900 black Marines were on the Iwo Kima beaches, many of which were ammunition carriers.
But Spike Lee lost the more important lesson in his PC world. The Battle of Iwo Jima cost the lives of 4554 Marines and 363 Sailors. Their blood was red.