The CAA (UK Civil Aviation Authority) application for a medical certificate asks for hair colour. Why? Are there any diseases / conditions more prevalent to particular colours? Most of the questions are seem to be rooted in common sense, but is hair colour really relevant?
Update in response to comments. Height, weight, sex, eye colour and race ALL have a relevance to medical conditions. Height and weight can indicate BMI and possible eating disorders, many conditions are gender specific, and some medical conditions are more common in different races (Cystic fibrosis is more common amongst northern Europeans, Sickle-cell anaemia is mostly a problem for those with African ancestors). Even eye-colour can (according to google) indicate a increased likeliness of a particular condition.
If hair colour really is there just for general identification purposes, then it's the only question on the form (other than name and CAA reference number) that has no medical purpose.