These three spin controls define the emissive color of the material. Setting all three controls to 0 would give a black color and setting all three to 255 would give a white color. The RGB values can also be set using the Windows Color palette control by pressing the Pick button beside the controls.
The emissive portion of a material describes how a surface emits light. For example, a lit sign or a light bulb have surfaces that emit light. This portion is not affected by lights in the scene.