buffalo soldier

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A member of one of the African-American regiments within the US Army after the Civil War, serving primarily in the Indian wars of the late 1860s.

from the GNU version of the Collaborative International Dictionary of English.

• A black soldier of the United States army who served in the American west in the late 1800's, often as an indian fighter, and usually as part of an all-black troop; -- the name was given by the indians due to their their kinky hair, and the name was believed also to be a compliment on their courage.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun US (military) (historical) An African-American soldier in the US Army, serving in one of a number of segregated units under white officers, in the period after the US Civil War up to the final racial integration of the US military, at the end of the Korean War.