Biracial or African-American son? 1950s

I'm searching for the birth family of my father. His name is David, he was born March 5, 1955 possibly in Roane or Knox County. He was adopted by African-Americans but he may be of mixed biological parentage, whether White, Black, Native American:confused: He could visibly fit in a variety of categories. People have thought he was biracial (black and white), Arab, Hispanic, Native American, etc. I believe his birthname was also David Michael or Michael David. Thanks!