> Well, to be honest, I am getting a little cobfused.
> The question for me is the following:
>
> I want to display a df3 - file that holds 16 Bit measuring values that 
> range
> from 0 to 65535. I want povray to display each value in a different color. 
> How
> is that possible to do ? Do I need a color map at all ?

There are several issues with what you are asking...

1) DF3 data describes a value for a 3D voxel,
many voxels will be obsured by the voxels in front
of them, to really see the values you need to
slice the cloud of voxels.

2) The human eye can barely distinguish between nearby
16 bit colors, but if you wish to create a large color map
the colors are linearly interpreted between entries in the
color map. So if you have a color map...
color_map {
   [0 Black]
   [1/255 Red]
   [2/255 Yellow]
   ...etc
}
then a value of $007F (127) will be a color rgb <0.498,0,0>,
a value of $017F (295) will be a color rgb <1,0.498,0>.

3. POV is capable of producing 16 bit images instead of
24 bit. Set the Output_File_Type=T in povray.ini to produce
targa format images, then add hf_gray_16 to your
global_settings. Then set up your pigment slice with
ambient 1 and no other lighting (no color map). The TGA
image will have the MSB in the red channel and the LSB
in the green channel. The preview shows just the red
channel. When loaded into a paint program, this is a striped
red-yellow-green image not very suited to human viewing,
but the color values are unique per DF3 value. POV can
load such TGA images as a height_field to show values
as a height.

// File: df3_slice.pov
// Vers: 3.6
// Desc: Orthographic DF3 slice
// use Output_File_Type=T in povray.ini
// use a square image ratio

#version 3.6;

#declare SliceAt = -0.5; // from 0 to -1

global_settings {
  assumed_gamma 1.0
  hf_gray_16
}

camera {
  orthographic
  location <0,0,1>
  look_at  <0,0,0>
  right 1*x
  up 1*y
}

box { // this box fits exactly in view
  <-0.5, -0.5, 0>, <0.5, 0.5, 0.001>
  texture {
    pigment {
      density_file df3 "spiral.df3"
      translate <-0.5,-0.5,SliceAt>
    }
    finish {
      ambient 1.0
      diffuse 0.0
    }
  }
}

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