Specular color 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.
In 3ds Max, you can set the specular color to match the diffuse color. This gives a matte effect, making the material appear less shiny.
Matching specular color to the diffuse color makes the surface less shiny.