There is already software that simulates a "Paint Ball" game. (People shoot each other with paint pellets; colorful splotches tell you you've hit someone.)
In the multiuser graphics game I'm thinking of, the paint you shoot is "intelligent"; you can supply a function for it, not just a single color; and paint comes in buckets, not just single pellets.
Users have a limited (but large) amount of paint that is keyed to them, performs their computation. (This is a nice metaphor because the computation available is in fact limited.)
There are a couple of ready-made filters to choose from, and there is a way of trading new filters.
The one with the most paint worn by other players wins. Users can implement booby traps that spray paint on other users lured into them, or attack others with painting weapons, or make paint that is so attractive that people voluntarily use it.
Paint wears off over time (or maybe can be washed off), but is layered; in particular, paint can be an effect on the layer below it.
(Taken to the next level, paint could be a transformation on the underlying 3D model of the user's avatar; shooting people could grow spikes on them, or make them smaller.)
There could be Spy Paint that reports its surrounding image to its owner; the physics of the game would have to be accurate enough to make sure that a little drop sees less than a whole bucket.-- jutta, Sep 10 1999 Is this for an online game, or some online/life hybrid? I can see a sort of "virtual paintball" where the players wear special glasses that overlay the paint, most of the weapons, and some identifier to let you know who else is playing.
Unlike traditional paintball, you don't have to go out into a secluded area to play; it would be more like an advanced version of that college assassination game played with spoons. Disadvantage is that someone is eventually going to try to evade a pursuer on the subway and fall on the tracks.-- bookworm, Jul 18 2000 random, halfbakery