One major problem I have and still can't figure out how to resolve is that at the point of "dye" deposit, there are some flickering pixels that are darker than they should be. I believe it has something to do with velocities being too high and the advection affecting them in an adverse way. Mike's article links to this fire simulation that is really neat. That one is much higher resolution and doesn't suffer from the brightness issue I have. Maybe with some more tweaking I can get a nicer result but I'm pretty happy about this as it is!