Umbrae pictae

Each shadow is the light of the other two lamps.

A ball floats over a pale floor under three lamps, red, green and blue, whose light adds up to a warm white. The ball casts three shadows, one per lamp. Block red and what is left is green plus blue, which is cyan. Block blue and the floor is yellow. Block green and it is magenta. Only where all three are blocked is the floor black.

The lamps are large, so each shadow is a dark core inside a soft rim. When the ball is low, the three cores overlap under it in black. As it rises, each core shrinks and vanishes, and above that height the floor under the ball is never dark again, only coloured, though the ball is still there.

Rendered offline from a single closed-form shader by the same module code a live page would run. No camera, and nothing leaves the machine.