I was writing a tutorial on the "Object Info" node of Blender Cycles and was trying to describe what happens when a color node is fed with numbers out side the interval (0, 1). I gave up and just said "strange things happen".
I know how to map values onto or clip them to the interval (0, 1) so I can usually get the effect I'm after but I'm curious and would like to understand how the color clipping works.
The image below show a grid of cubes in the XY plane. They all have the same material as shown. The larger wire frame cube goes from (0, 0, 0) to (1, 1, 1). There are no lamps and the world surface color is set to (0.051, 0.051, 0.051) (default start up).
Outside the wire frame cube all the little cubes seem to act like emission lights. I think this is related to the answer to this question.
What I don't get is the diagonal line of black cubes. For example rgb(2, -2, 0) gets mapped to black but rgb(2, -1.75, 0) gets mapped to red. There are other lines of black cubes if we move the grid of cubes up in z.
For example all of the following cubes are black (-1, -1, 2) , (0.5, -1, 0.5), (-1, 0.5, 0.5), (0.5, 0.5, -1) , (2, -1, -1) (2.5, -3, 0.5).
Can anyone explain how this works?