I'd be willing to bet, but haven't proved by actually doing it, that it's the activated charcoal/zeolite or other organic bonder (it isn't all charocoal) and I could make something with fish tank zeolite or the like that will remove the color, but not have small enough pore size to stop the pathogens. For this reason I actually personally thing the color stuff is dangerous marketing claptrap. color is removed by reaction, not filtering. while pika might not discount a cartridge because it doesn't react with food colouring, I wouldn't believe a cartridge actually works just because the cartridge does react with food coloring.