[RUNGSI]

Well you can edit each weapons muzzle flash, rate of fire, sound directory and such in its .tik file.
Most of your work can be done there. Now as for the paintball itself, you could cheat a little and recolor the tracer to that pink color and set tracers to show on every shot. it would look like a pink streak.
That would be a way to get you started.
you can however make a "paintball" and use it as a projectile and add speed and gravity to have it drop.
again, all edited in the weapons tik files.

Hum, well sounds like you have some work to do, so i will leave you to it.