I'm pretty flat-chested (34aa) so it's hard for me to say how the sizing runs on this top for others. to me, it's a slim fitting but not tight, true to size t-shirt. i tried the xs regular (dressing room photo) and the small petite (other photo) and i'd say the main fit difference was in the shoulders. the small petite fit me better in the shoulders (xs petite wasn't available). also the neckline of the small petite came up a little higher. the white is a slightly dingy off-white but i think the