black is the result of no light reaching your eye, because all sight is based on light. the eye does not see objects, only the light that bounces off of them.
if a "black" object reflects 0% of light that reaches it, even if it recieves 100% of the light that has a possibility to reach it, it reflects back 0% of that, which makes it appear black.
if there is no light to begin with, even objects that are "white" will appear black, because, while a highly reflective white object reflects close to 100% of the light that strikes it, reflecting 100% of 0 is still 0 is still black.
when there is visible light present, even a pure black object will not appear to be pure black, but it will appear to take on the color of the particles in the air that are between the eye and the object. this is half of the physical reason for "make your darkest regions match the sky as they get farther away," although that is extremely simplified.
contrary to what i learned in art class, i now know from physics that pure white and pure black exist in nature all the time because of the atom's quantum properties. basically, a unit of energy must pass through an object to excite its ring of electrons, which absorb the energy, and then release that energy back out; thats how we see an object's color. atoms which release less energy back when they drop down are percieved as darker objects. the energy that is not released as light stays with the atom as heat which is why dark objects tend to become hotter.
this quantum thingy makes two common artistic ideas false -
"there is always at least a little visible light" - No! any time when there is not enough energy to reach a quantum, no light is reflected. Also, the light reflected has to be enough to reach a quantum inside your eye. we see only a fraction of the light that was originally emitted! pure black is everywhere.
"there is never pure white because it is always reflected" - No! because an atom can only absorb certain quantities of light, there will always be light that - get this - passes straight through it (atoms are 99% empty space). Pure white is seen any time there is enough energy - emitted or reflected - to maximize the amount of light the eye can understand. pure white is everywhere.
thing about this - the molecules that make humans, in particularl our eyes, are so sensitive that when this happens there is so much energy that the atoms keep giving off light and heat and keep getting hotter and hotter until they begin to break down the molecular structure, resulting in a sunburn on your skin, or blindness. the effected parts of the eye though are shut off if there is far too much light, so as to preserve the functions - and there you get though ghost images on your eyes whenever you look at a particularly bright light. please dont go looking at the sun to see if it it is actually white >.<
