After WWI, my great grandfather (a white man) went to a military school headed by a black officer. Was this at all common?

Greetings! I recently got to read through my great grandfather’s unfinished WWI memoirs. My great grandfather enlisted in the Minnesota National Guard during the war, and was shipped overseas to fight in France, eventually receiving a battlefield commission as a Second Lieutenant. After the ceasefire, he was sent to a military school in France where the lead instructor was a “famous Negro officer” named Colonel Moss. This was surprising to me, as I know how deeply segregated the army was during the War, and that General Pershing in particular was a deeply bigoted man. My great grandfather noted that Colonel Moss was a severe (though usually, it seems, quite fair) disciplinarian. How common was it for black troops to be supervising white soldiers? And who was Colonel Moss?