Classicly

A race distinction in the law is a requirement imposed by statute, constitutional enactment, or judicial decision, prescribing for a person of one race a rule of conduct different from that prescribed for a person of another race. If, for instance, a Negro is required to attend one public school, a Mongolian another, and a Caucasian a still different one, a race distinction is created, because the person must regulate his action accordingly as he belongs to one or another race.

Or, if a person, upon entering a street car, is required by ordinance or statute to take a seat in the front part of the car if he is a Caucasian, but in the rear if he is a Negro, this rule is a race distinction recognized by law. Again, a race distinction is made by the law when intermarriage between Negroes and Caucasians is prohibited.