Sometimes, but only by the general perception of the defendant and that doesn’t require any kind of strict scientific measurement. You’re still missing the key fact that discrimination is based entirely on the offenders perception – the reality of any victims is irrelevant. There might not even be an actual victim; a shopkeeper putting up a “No dogs, no blacks, no Irish” sign would be breaking discrimination law even if no black or Irish people see it.
Skin colour isn’t the same thing as race. Western European whites could discriminate against Eastern European whites, European Spaniards could discriminate against American Hispanics, West African Blacks could discriminate against East African Blacks etc. And while it would be an odd situation, it’s perfectly viable that a person could discriminate in favour of other races against their own, say a white employer choosing to employ a black candidate over a better white one to make their racial statistics look better.
Anyway, legally, “racial discrimination” will tend to cover discrimination on the basis of nationality, creed or culture too.
I agree that as a fundamental core principle, “race” as a division between human beings is fairly meaningless and tends to cause more harm than good. It remains a concept that lots of people hold to though and continue to actively discriminate against others based upon their perceptions and the law continues to account for that.
I agree that within the same race, color can vary. However, color and culture, at least as it applies to discrimination, must have a racial component. Take these examples:
White man comes back from vacation with a dark tan. Gets fired. Sues for color discrimination, gets nowhere. His color must be associated with race in order to have 'bite'.
White man eats a hot dog in front of his boss, gets fired the next day. Sues for culture discrimination (choice of foods). Gets nowhere. The culture practiced must be associated with a 'minority' race in order to have bite.
These would change if the darker color was natural skin tone, or if the food was Mexican and consumed by a Hispanic. Racheal Dolezal's hair, skin tone and cultural practices were entirely dismissed because she lacked the underlying genetics (or 'heritage' or another something that people can't do a thing about themselves). More importantly, the visual cues we got from Dolezal (hair style was one) were associated, correctly or incorrectly, with the black race.
Therefore, only certain hairstyles can be used as a basis of discrimination, or only certain foods / culture / language. When does a food, cultural practice, or hairstyle become important enough to matter in a discrimination suit? English doesn't matter, neither do hot dogs. Bring in Spanish and chimichangas, and the story changes radically - it's because we associate those cultural practices with Hispanics, even though any race is perfectly capable of speaking Spanish or consuming a chimichanga.
My point is that we need a scale by which traits of food consumption, language spoken, hairstyle and appearance would qualify as important in a discriminatory case.