Having white hair helps prevent getting questioned about what you are doing while measuring. When the police or park rangers see a couple disheveled, white haired old guys on bikes, wearing yellow vests, stopping frequently to write something on scraps of paper, they usually just shake their heads. This is especially true when the old guys are dressed in several layers of standard work clothes, jeans and wearing bulky ski gloves; not the high tech lightweight gear they are used to seeing on riders.