"Well, you sorta can..." See: Frisk's striped shirt and the pants and the green scarf. They've been wearing those for literal years now, and it's amazing they're so intact still--maybe it's castle magic...though when Frisk was tossing them off in the back room, the blue was starting to look awfully faded.

"...but more's nice." They clap their hands once, sharply, rocking more on their feet enough to make the skirt ripple. "What's your favorite color...s?" The copy might have a different favorite.