The Paint Material Type is used when a plain, non-metallic paint appearance is desired. It provides a quick way to set a base color and then control the clear-coat on top.
Color Color is your base layer of paint and the overall color of the material. Click the color thumbnail to open the Color Picker and select your desired color.
Roughness This will add microscopic levels of imperfections to the surface of the material when the values are increased. When this is set to 0, a material will appear perfectly smooth and polished. When the value is increased, the material will appear more rough as light is diffused across the surface.
Samples A low samples setting (8 or lower) will tend to make the surface look more noisy, which will give a more imperfect and rough look. As you increase the value, the noise will smooth out and provide a more evenly distributed roughness.
Refractive Index This controls the intensity of the clear-coat. 1.5 is a good general starting point. If a more shiny paint is desired, increase the value. Bringing the value down closer to 1 reduces the clear coat effect. This can be useful for making a matte finish.