Neon Eggs are items that are only seen in Mario & Luigi: Superstar Saga. They are special eggs that are laid by Yoshis after they have been fed Bean Fruit. They come in seven colors: green, purple, blue, red, orange, azure, and yellow.
The Neon Eggs were gathered when the Mario Bros. fed Bean Fruits to different-colored Yoshis. Boddle used them to decorate the sign for the Yoshi Theater, and traded them with the Mario Bros. for the Beanstar.