is the color of highlights on a shiny surface. The highlights are reflections of the lights that illuminate the surface. For a naturalistic effect, set the specular color to the same color as the key light source, or make it a high-value, low-saturation version of the diffuse color.
Changing specular color tints highlights on the shiny surface of the spacecraft.
Matching specular color to the diffuse color makes the surface less shiny.