This isn’t about “what is the physical difference” that was covered in an earlier column, but about the fact that some people have preferences.
For example, in fast-food joints, if you order, for example a “two- [or three-]piece chicken” meal, a clerk might ask “white or dark?”
This might be more of IMHO, but I’ve never been sure of why some people prefer one over the other–and as someone who has little sense of taste–either gustatorially or culturally–there’s not enough of a difference to me to cause me to have a preference.