The big problems with paint grenades is all of them try to throw liquid. Tippmann's "bouncing betties" are just tubes of surgical tubing that spray streams, the old M-85s with their little blackpowder charges exploded a "baggie" of liquid paint, and so on.
And the problem with that is that spray dissipates. With nothing to hold it together, a jet of paint turns into a cloud of mist in a relatively short distance. The mist both lacks mass for distance, and cohesion to form a mark on the target.
My seal-bomb experiment (which I fully admit was done more for fun than an actual experiment ) basically vaporized the balls in the blast, leaving little but mist to hit the targets which were hardly two or three feet away.
Your "colander" idea, while interesting, would do the same thing- each "jet" of liquid would turn into a cloud of mist within just a few feet. Counterintuitively, you'd likely get more "range" with a slower propellant blast than a faster one. A Fast one would force the paint out in a spray, a slow one would ease it out in a stream.
Now, to improve on that:
First, instead of a colander, we give it a shell thick enough the holed become jets. A longer "jet" passage helps keep the stream coherent longer- that's essentially how most spray bottles work, so you have both a "spray" a "stream" setting.
Or, keep the thin shell and solder on a bunch of "spines"- short chunks of small-diameter tubing. Not really workable from a production or use standpoint, but for a test it'd do fine. For best range/distance, maybe even tapered tubes, like little firehose nozzles.
Then, put a balloon or other bladder in the middle of the shell, uninflated. Fill the shell with paint, and hook a valve of some sort to the bladder.
You'll need something relatively slow- a somewhat-metered dump from a 12-gram, maybe, but not a "blast" like from an explosive or sodium azide. The bladder should inflate within about a second or second and a half, with enough pressure the paint is forced out the tubes/jets, but not so much pressure the bladder or the shell ruptures.
Again, not really workable from a marketing or sales standpoint- each grenade would probably cost $80 and take half an hour to clean and refill.
So what we need, as we talked about a few weeks ago, is something that can throw complete paintballs. We need shrapnel not spray or mist.