Alan - We are clearly talking about two different individuals. The confusing factor is that both men had a wife named Emma. However, the black individual lived in Dinwiddie County, VA, while our 1st Alabama Cav. John Wesley Evans lived in Danville. Depending on where he was actually born (Virginia or North Carolina) there are several white male children named John Evans who were 5 years of age in 1850, and 15 years of age in 1860.

1880 Census
Name: John W. Evans
Age: 35
Birth Year: abt 1845
Birthplace: Virginia
Home in 1880: Dan River, Pittsylvania, Virginia
Race: White
Gender: Male
Relation to Head of House: Self (Head)
Marital Status: Married
Spouse's Name: Emma Evans
Father's Birthplace: Virginia
Mother's Birthplace: Virginia
Occupation: Carpenter

1910 Census
John W Evans
Age in 1910: 56
[66]
Birth Year: abt 1854
[abt 1844]
[1844]
Birthplace: North Carolina
Home in 1910: Danville Ward 5, Danville (Independent City), Virginia
Race: White
Gender: Male
Relation to Head of House: Self (Head)
Marital Status: Married
Spouse's Name: Emma Evans
Father's Birthplace: North Carolina
Mother's Birthplace: North Carolina

1920 Census
John W Evans
Age: 75
Birth Year: abt 1845
Birthplace: North Carolina
Home in 1920: Danville Ward 6, Danville (Independent City), Virginia
Race: White
Gender: Male
Relation to Head of House: Head
Marital Status: Married
Spouse's Name: Emma W Evans
Father's Birthplace: Virginia
Mother's Birthplace: Virginia