(I'm sure many of you have seen this before)

We have rgb, rgbf, rgbt, rgbft,

..... and then we have colors that just aren't there at all.



There is:
a cyan disc
a magenta disc
and a blue vesica piscis
on a plane of blue lines

Imaginary colors:
there is no "dark blue", "green", "red",
and there is absolutely no yellow.

Interestingly, the illusion is instantiated by the addition of BLACK.

Something to think about the next time you ponder why your render "looks weird".

- BE

Try it!

// Color Illusion
// Bill "Bald Eagle" Walker
// 2026-03-29

#version version;
global_settings {assumed_gamma 1.0}
light_source {<10, 20, -50> rgb 1 shadowless}
sky_sphere {pigment {rgb 1}}
camera {
 location <0, 0, -2>
 right x*image_width/image_height
 up y
 look_at <0, 0, 0>
}


#declare ShowIllusion = yes;


#declare BlueLines =
pigment {
 gradient x
 pigment_map {
  [0.0 rgb z]
  [0.5 rgb z]
  [0.5 rgbt 1]
  [1.0 rgbt 1]
 }
}

#declare BlackLines =
pigment {
 gradient x
 pigment_map {
  [0.0 rgb 0]
  [0.5 rgb 0]
  [0.5 rgbt 1]
  [1.0 rgbt 1]
 }
}

#declare LineScale = 0.02;

plane {z, 0 pigment {BlueLines scale LineScale}}

#declare Imaginary =
intersection {
 plane {z, 0 pigment {BlackLines scale LineScale} translate -z*0.001}
 sphere {x*0.25, 0.5 pigment {rgbt 1} rotate z*330 translate z*0.01}
}

#if (ShowIllusion) object {Imaginary} #end

difference {
 disc {x*0.25, -z, 0.5 pigment {rgb y+z} rotate z*90 translate z*0.01}
  sphere {x*0.25, 0.5 pigment {rgbt 1} rotate z*210 translate z*0.01}
}

difference {
 disc {x*0.25, -z, 0.5 pigment {rgb x+z} rotate z*210 translate z*0.01}
  sphere {x*0.25, 0.5 pigment {rgbt 1} rotate z*90 translate z*0.01}
}

intersection {
 disc {x*0.25, -z, 0.5 pigment {rgb z} rotate z*90 translate z*0.01}
  sphere {x*0.25, 0.5 pigment {rgbt 1} rotate z*210 translate z*0.01}
  sphere {x*0.25, 0.5 pigment {rgbt 1} rotate z*90 translate z*0.01}
}

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