It depends on the lighting conditions and local color, but the terminator and midtones should both be highly saturated for white skin. The ambient light in the shadow could be highly saturated, provided the source of ambient light is of a similar hue to the local color.>>4923208>shadows will always be less saturated
Not so. It all depends on the environment. If the ambient light is complementary or close to complementary to the local color of the object, then yes, the shadows will get desaturated. And if you are actually using your nightvision in a dark area, then yes, everything will approach grey, because your rod cells cannot really distinguish color.>1) saturation darkens value
This could be said to be true, depending on what you mean by 'value', but is isn't strictly speaking true. If you mean the perceptual value of a color, then yeah you could say in certain circumstances, increasing saturation decreases value, but with the way these terms are generally used, saturation and value are two separate parameters.>Highlights and reflections can't be saturated
Also not true. In nature, highlights tend not to be saturated because in nature light is very white. If you were casting a pure red light on a scene, you would have saturated red highlights, for instance.>and reflected light is always weaker
This is technically true in that everything absorbs and/or refracts light a little bit, but it isn't quite how you mean it. In the case of reflections and specular highlights, most of the light is actually being reflected, which means the the color will be extremely close to the color of the light source.
Light and color are excessively complicated, so sorry if some or all of this post was unclear.