stupid question re: brians sweater on letterman

debating with my friend... at first i thought the black sweater he was
wearing had a white stripe around the collar, but after watching the
clip again, it looks like that may just be a white vneck underneath
with another shirt under that. weird. if it is a sweater with a white
stripe, anybody know what kind it is? sorry, i know this is very lame.

it looks like a v-neck with another shirt under it