When we look at an object we can differentiate between darker or whiter object. We say that a dark object has a low value while a white object has high value. From a physiological point of view we can say that the rods (black-and-white receptors) determine the value. We can also separate between different colors, a separation that is done by the cones (color receptors). The different colors (e.g. red, green and blue) represents different hues. However, we can also differentiate the color with an certain hue group based on color saturation or chroma.
Of the different parameters, the value is probably the most important simply because we have much more rods than cones in our eyes. Dental shade guides are therefore often arranged in an order that is based on value rather than hue and croma.
Object that appear to be color matched under one type of light may appear different under another light source. This phenomen is called metamerism. Metamerism is caused by differences in wavelength distributions among different light sources. For example, a surface may contain a molecule that might be stimulated by a certain wavelength to give of a certain color. When this surface is exposed to light that does not contain that wavelength, the color is not produced, while in another light environment where the needed wavelength is present, the previously hidden color is released. This phenomena is very important to consider when dental restorations are made becuase depending on the light environment the color might look differently.