The RGB Spectrum node outputs the color specified in the Color parameter.
In figure 1 an RGB Spectrum node is connected to the SpecularAmount of specular reflection, or the mirror-like reflection of light photons at the same angle. Used for transparent materials such as glass and water. parameter of a Glossy materialUsed for shiny materials such as plastics or metals..
Figure 1: An RGB Spectrum node is connected to the specular channel of a glossy material.