Well, I made a mistake: the prop material definitions should be outside the figure block:

{
version
{
number 4.01
}
figure
{
material body
    {
    KdColor 0.980392 0.980392 0.980392 1
    KaColor 0 0 0 0
    KsColor 0.843137 0.843137 0.843137 0.1
    ..............
    }
}

prop right_eye
  {
material right_eye
    {
    KdColor 1 0 0 1
    KaColor 1 0 0 0
    KsColor 0.984314 0.084314 0.084314 0
   .................
     }
  }

}

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