In 1959 underwear is white, at least for males. For females pastels are optional. Early in adolesence, Jane's first bra would have been a "training" bra, though what is being trained would not be specified. Snavely is bare-chested here since T-shirts are now outerwear, no long called under-shirts.

Snavely's shorts are of the type called "briefs," which he unconsciously associates with rabbits, since recently reading this passage in "Rabbit Run" by John Updike:

As he ("Rabbit" Angstrom) comes back across the room Ruth laughs from the bed. He asks, "What's the joke?"

"In those damned underclothes you do look kind of like a rabbit. I thought only kids wore those elastic kind of pants."

Old-fashioned masculine boxer shorts give way to tight briefs, somehow suggestive of girls' underpants. Or little boys' undies. Another step in the slide toward unisex.