To add textures, use the hierarchical nature of the file format and add an optional TextureFilename data object to the Material data objects. The Material objects now read as follows:
Material RedMaterial {
1.000000;0.000000;0.000000;1.000000;; // R = 1.0, G = 0.0, B = 0.0
0.000000;
0.000000;0.000000;0.000000;;
0.000000;0.000000;0.000000;;
TextureFilename { "tex1.ppm"; }
}
Material GreenMaterial {
0.000000;1.000000;0.000000;1.000000;; // R = 0.0, G = 1.0, B = 0.0
0.000000;
0.000000;0.000000;0.000000;;
0.000000;0.000000;0.000000;;
TextureFilename { "win95.ppm"; }
}