The paint bloon is a messy parent of the pink bloon. It leaves paint on the track that it travels on. This paint will slightly speed up any bloons that travel over it, whilst making the multi-hit bloons slightly weaker. It moves slightly faster than a Pink Bloon due to being covered in said paint.
Since it moves slightly faster then a Pink Bloon, it could be implied that this is a Pink Bloon that's been covered in the paint that is spreads on the track.