What @thehen said is applicable, if you want computer-color blending.
I suppose you want to blend liquids as liquids should blend - i.e. as we all learned in 3rd grade art class (yellow and cyan = green, white + color = lighter color).
I was actually researching this a few weeks ago. It turns out that as far as I can see, nobody has even discovered a reasonable algorithm to accomplish this. It goes into the terrible realm of color spaces.
Let me know if you get it to work!