Whenever lighting is enabled, the color of our geometry must be given as a material. The material color properties are given for calculating ambient, diffuse and specular reflections. For our cube, we set only an ambient and diffuse color. When the color is the same for both, we use the constant GL_AMBIENT_AND_DIFFUSE. This does not have to be the case; we can set separate colors with the constants GL_AMBIENT and GL_DIFFUSE.