The comment that 'must be fairskinned' is a form of prejudice is not entirely true. It may just be a preference. As I said previously it can be like a choice of car colors.
When does it become prejudice?
No one can say for sure, unless there is an overt act or sentiment that causes or has the intent to cause any form of injury, be it physical, emotional or psychological.
Otherwise it is just predilection or discrimination, in that the person is exercising his or her free will to make a choice/discernment based on his or her desires, wants and/or needs.
There is a danger in using terms like 'prejudice' and 'discrimination' due to the colloquial nature the terms have assumed in that the 'knee-jerk' response is one of racism/hatred, etc. I hope people recognize the form in which I am utilizing the terms.