hi! do you have the code you tried already that you want to share? are you working with processing or p5.js?
I think it’s not a dumb question at all and as you noticed the color is set globally (color depends on the density value). I don’t have a quick solution for you, but I can give you suggestions. 1) if you think this is a challenge for yourself to implement it, my guess is that you need to prepare Fluid objects separately for red, green and blue channel and mix them. It should not be a terribly difficult task, but it requires some patience 
or 2) if you just want to use a fluid simulator, there is pixelflow for processing
I never tried any fluid simulator for p5.js but there are bunch of javascript fluid simulations I guess (I appreciate if anyone has suggestions!)