Daft question??

Does the black hair grow quicker than the white? Or is it just that the white is the undercoat and therefore flatter to the body? Logan's black bits are longer and fluffier than the white on his body. Looks like 'just got out of bed hair' - the chiropracter commented on how cute his 'tufty' bits were and a few people we've met on walks have remarked on it.