Take a 'White' person, for instance: is a White American the same as a White Englishman, or a White Australian? What about a White Frenchman? These are all classified as 'White' but could potentially be vastly different in terms of diversity.
The same argument could be made with the other ethnicities. The 'Asian' category -- are they Chinese, Japanese, Filipino..? Or an American Asian immigrant -- Chinese-American, etc.
If you're aiming for diversity that's representative of your customer base, then surely your measure of ethnicity has to be more granular.