Problem might be paint viscosity, if applied in any other way than roller or spray it is highly likely that it will cause the paint to run down.
Ballons needs somethink sharp to pin thru the rubber surface, so throwing then might have opposite effect. From my childhood i can propose to but 3x dozen eggs, remove the content by punching two tiny holes at the oposite egg ends, blow through to remove egg content, fill with paint, block both hole and off you go! After collision, egg shell bits can be romoved with tweezers.
Nice colour choices and the background cloth will make great seat covers!