Sena

Keep the cup at room temperature and away from any heat. They grow alarmingly fast when warm.

Nothing has gone wrong. Feeder hornworms are raised on a prepared chow rather than on plants, and that chow is what makes them that turquoise blue. The ordinary green is what you get when a hornworm takes in plant pigments instead, or when the chow changes, or just batch to batch variation between suppliers.

The restless ones are the more interesting part of your post. Wandering plus slowing growth plus going off the chow usually means they are getting ready to pupate.