There were several African-American units that served on Omaha and Utah beaches, but they made up only a very small percentage of all troops. Most of the African American troops actually served on Utah Beach. (About 1,200 at Utah, vs about 500 at Omaha) Probably the best-known unit was the 320th Barrage Balloon Battalion (VLA) Most of the battalion served at Omaha Beach, while one battery served at Utah Beach.

Other African American units on D-Day included the 385th Quartermaster Truck Company, the 490th Port Battalion, the 582nd Engineer Dump Truck Company at Utah Beach, and one section of the 3275th Quartermaster Service Company at Omaha Beach.

Sources:

http://www.longshoresoldiers.com/2011/01/history-of-490th-port-battalion-in-wwii.html?m=1 http://www.army.mil/article/119639/All_black_balloon_unit_served_with_distinction_on_D_Day/ http://www.qmfound.com/black_service_units_in_combat.htm