Look at it another way. What is the goal of their product? A person should be able to sit down, and draw something. That person has a model in his head of what the drawing should look like. He picks and mixes colors to achieve this according to his intuition. So the goal of the program is to match human intuition, not to match reality. Why would real world paint be the optimal painting tool? The best way to match human intuition is to base the behavior of the program on data collected from human intuition.