The Germans certainly had colonial units throughout the war. As only one example, they had in Cameroon by 1914 a colonial troop, the Schutztruppe, that had 200 German officers and NCOs, and 1550 African Soldiers. Though these forces were designed for internal control, not fighting major campaigns, they are an example of the extensive German colonial forces. These forces in Cameroon were used to fight both the French and the British in August/September 1914, and fought well, though finally being defeated. The German colonial garrison in SW Africa (Namibia), in contrast, had no native black troops, though its total size was about 140 officers and 3000 soldiers-- the troops were white volunteers, most with previous military service. In German East Africa (Tanzania, Burundi, Rwanda) at the outbreak of war, the Shutztruppe had about 260 Europeans and about 2500 African troops. In all of these colonies, there were also extensive gendarmeries, which after the outbreak of war were incorporated into the schutztruppe. As an example, the numbers in the German forces in East Africa by the end of the war were about 3000 Europeans and about 11,000 African fighters, plus untold thousands of African laborers. I am unaware of any use of these troops in Mainland Europe, but there was extensive fighting throughout Africa in which they played a major role (on both sides, actually, as African Forces were also present in French, British, and Portuguese armies in Africa). Best popular reference I have found is: "The Great War in Africa", by Byron Farwell, Norton, New York 1986.