This may be a silly question, but how does an object's color factor into the way it reflects light? If a ray hits a colored surface like this, then its reflectivity (diffuse vs. mirror) will affect whether the ray bounces straight off or scatters. But when does the color come into play? Do materials have color opacities/strengths as part of them? For example, a mirror can have (basically) no inherent color, or it could be a red-tinted mirror. If it's red-tinted, it can be slightly diffuse/blurry, or still very sharp. The more diffuse something gets, the more it seems to show its inherent color. You couldn't have a diffuse teapot with no color--it would be white or black.
Unity's built-in materials have the properties "Metallic" and "Smoothness," which seem related to this issue. How do these work, from a rendering perspective?