I just came across this description of a soldier in a USCT unit. I suspect the description of complexion
as Yellow describes a Mulatto. I know Copper was sometime used.

Was this common, how some light skin Colored troops were described at the time? I believe Copper was sometime used.

Robert Blue, Private, Company H, 13th U. S. Colored Heavy Artillery, enlisted November 16, 1864 at Greenupsburg, Ky. for 3 years, recorded present at the July/August, 1865 muster, transferred from Company B, 121st U. S. Regiment, Colored Infantry, June 23, 1865[?], description, 40 year old Laborer, born in Mason County, Ky., black eyes, black hair, yellow complexion, mustered out November 18, 1865

Compiled Military Service Records of Volunteer Union Soldiers Who Served the United States Colored Troops