Not that we're assholes or anything. Just, dirt on your gear is one thing but paint is a totally different thing.
As for something to help you out:
Should be cheap so that if in the off chance the grenade gets lost you're not out a terrible amount of money.
Minimum 10 ft. spray (in all directions) is ideal.
I guess paint to fill it up with (you could probably buy paint by the barrel and sell to people in litre bottles or something.
Colours.... Depends on who you're selling to. Woodsball and Milsim PB players will probably be more attracted to earthy/neutral tones. While speedball players might be more into the neon and bright colours. You could probably have some sort of grenade "cozy" in green/tan/black and make the grenade a bright colour to aid in finding it afterwards.
Other design considerations, simple system that even a 12 year old could use with a minimum number of parts and minimum maintenance required (ie. if there's possibility of paint drying inside and gumming up the delivery of the paint to the area you're throwing it think of something to take care of that).
You're probably also looking to run your system via 12 gram CO2 cartridges (possibly something more powerful) since you'll need a lot of pressure/power to push a medium sized amount of paint in all directions for 10 feet.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE