Inside-Out is a quality that bloons can have. Bloons with this quality all look like red bloons, but this is because the order of what bloons contain what other bloons is the opposite of what it normally is. Therefore, all of the bloons will look like red bloons at first. However, when you pop one of these bloons, it may turn out to have a blue bloon inside it, which might have a green bloon inside it, and so on. When you pop the final inner layer (whatever color would ordinarily be the outer layer), the bloon will be gone.