I have been reading Nikki Flynn's superb account of her life as a spanking model "Dances with Werewolves". In one of the most arousing passages, Nikki explains that her favourite outfit for punishment is the traditional English schoolgirl uniform of white blouse, tie, pleated skirt. white socks and white knickers.
she also says that she loves being bent over "skirt up, knickers down" for a caning from a headmaster or headmistress.
She has a large collection of outfits and says that when packing for a shoot she always takes at least four pairs of white school knickers. This is because, as she says "nothing reveals arousal like white cotton".....as these pictures show:
She says that during shoots she had to change her knickers a couple of times as they became wet enough for her arousal to be very evident!