I just watched a TEDTalk video about Tom Shannon, an artist with Parkinson's disease who creates paintings using a big pendulum to squirt paint onto a canvas on the ground (the motion of the pendulum can be wholly contained within the canvas or, more commonly, sweep widely beyond the canvas). He started in the 1970s with a pendulum and a single color of paint. The paint flowed freely and he had real trouble refilling it while it stayed in motion. He now has a pendulum with six or eight colors whose release is remote controlled (mechanical clips hold the rubber nozzles shut and he can control how far each one opens at any given time).
It was at the moment he mentioned he wanted a pendulum with six colors that an idea hit me. I would like to see a painting, sculpture, or animation that utilized the primary colors across the three planes of our dimension. In animation, for example, you would follow a flowing line like a dribble of paint as it flowed across a rough surface. The color of the line would vary based on its current vector, with correspondingly greater amounts of blue, red, or yellow as it headed further into the x, y, or z planes.
Or, to put it another way, imagine a black dot in the middle of an empty white universe. If the dot moved left, it would leave a blue streak. If it moved up, it would leave a red streak. If it moved away from you, it would leave a yellow streak (but you would only see it as a dot). If, while moving left, it then turned in a shallow curve upwards, you would see the blue streak slowly turn purple then red as it flowed through the curve and moved upwards. If it then moved away from you while still going up, you would see an orange line (red + yellow).