I've heard interview from white Americans on the subject. One was an infantryman under fire and was saved by an all-black tank battalion. He said it was so strange seeing a black man stick his head out and ask if they were alright. Would the French, Belgians, etc. Have similar reactions? How were these guys seen by the locals?
I know that black and Indian colonials served on the western front of WWI, so it may even be something the Europeans were more used to.
The French were familiar with African-American units from the first World War. The 93rd Infantry Division fought as part of the 4th French Army. Source: http://edsitement.neh.gov/lesson-plan/african-american-soldiers-world-war-i-92nd-and-93rd-divisions
Units like the 369th "Harlem Hellfighters" Infantry Regiment (part of the 93rd ID) were highly decorated by the French; many earned the Croix de Guerre. Source: http://www.militaryhistoryonline.com/wwi/articles/fightingforrespect.aspx
France was apparently welcoming of these soldiers, and I have heard stories that some African American soldiers liked the comparatively better treatment they received in France that they left the US and went to live there. See this prior thread for some additional commentary on how they were treated: http://www.reddit.com/r/AskHistorians/comments/1yzv72/africanamerican_soldiers_in_france_during_wwi_how/
France would have likely certainly welcomed them during WWII, though the US military was still segregated during WWII, and black units may not have been given "glory" assignments, like liberating Paris.