I cut out circles of each color and used double stick tape to tape them to the bottom of each cup in the carton.
LM has loved playing with this activity. In fact, when he woke up this morning, it was the very first thing he wanted to do! And he has played with it all day. He will open it, take out all the eggs, put them back in, close it, carry it around, open it, take out all the eggs, put them back in, close it . . . and on and on. It's a big hit!