Here's an example or two of using full-colour pigment functions. This
example shows how to do a fake MC Escher "Circle Limit" effect, using
stereographic projection. True "Circle Limit" pictures use hyperbolic


(angle-preserving), FWIW.

// Persistence of Vision Ray Tracer Scene Description File
// File: PigFunc.pov
// Vers: 3.6
// Desc: Pigment function demo
// Date: 2005.02.19
// Auth: PM 2Ring
//
//  -D +A0.1 +AM2 +R4
//  -F -A0.4 +AM2 +R1
//

#version 3.6;

global_settings {
  assumed_gamma 1
}

camera {
  location <0, 5, -1> * 2.4
  look_at  0
  direction z

  angle 40
}

light_source {
   <0, 2, -1> * 50
   rgb 1.75 // 2.25
}

//---Color Maps--------------------------------------------

//Make a color_map from a0 to a1
#macro CMRange(a0, a1)color_map{[0 a0][1 a1]}#end

//Make a color_map from Black to a
#macro CMFull(a)CMRange(rgb 0, a)#end

//---Stereographically projected
pigment!-----------------------------------------

#declare R2 = 8.8;
#declare f_proj = function(x,z){R2/sqrt(R2 - min(R2-1E-12, x*x+z*z))}

#declare TestPig = pigment{hexagon rgb<1 .9 .5>, rgb <.85 .5 .6>, rgb <0 0
...8>}

#declare f_Pig = function{pigment{TestPig}}
#declare f_Pig1 = f_Pig;

//Turn a pigment function into a real-live pigment!
#declare PigRGB0 =
pigment{
  average
  pigment_map {
    [1 function{f_Pig(x,y,z).red} CMFull(red 3)]
    [1 function{f_Pig(x,y,z).green} CMFull(green 3)]
    [1 function{f_Pig(x,y,z).blue} CMFull(blue 3)]
  }
}

//And now, with projection!

#declare f_X = function{x*f_proj(x,z)}
#declare f_Y = function{y}
#declare f_Z = function{z*f_proj(x,z)}

#declare PigRGB1 =
pigment{
  average
  pigment_map {
  #if(0)
    [1 function{f_Pig(f_X(x,y,z), f_Y(x,y,z), f_Z(x,y,z)).red} CMFull(red
3)]
    [1 function{f_Pig(f_X(x,y,z), f_Y(x,y,z), f_Z(x,y,z)).green}
CMFull(green 3)]
    [1 function{f_Pig(f_X(x,y,z), f_Y(x,y,z), f_Z(x,y,z)).blue} CMFull(blue
3)]
  #else
    [1 function{f_Pig(x*f_proj(x,z), y, z*f_proj(x,z)).red} CMFull(red 3)]
    [1 function{f_Pig(x*f_proj(x,z), y, z*f_proj(x,z)).green} CMFull(green
3)]
    [1 function{f_Pig(x*f_proj(x,z), y, z*f_proj(x,z)).blue} CMFull(blue 3)]
  #end
  }
}

//---Scene--------------------------------

cylinder{
  -.1*y, .1*y, 3
  //open
  pigment{
    PigRGB1
    //PigRGB0
    //TestPig
  }
}

background{
  //rgb<0.035, 0.27, 0.67>
  rgb 0
}

//-------------------------------------------------------

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