The wonderful precision instrument that is the human eye can do some pretty remarkable things in coordination with the brain. Adapting to see in the dark, being able to process depth perception and the ability to distinguish even the slightest variations of color are some the very things that the eye and brain can do. The way our eye sees and processes color is conceptually simple but very important.
The brain and eyes are connected by the optic nerve, which transports the images of the world we see to the brain for processing. In the eye, there are two different types of photoreceptors- rods and cones. The job of the rods are to allow some capabilities of seeing in dim light conditions or at night, the cones, on the other hand, are used in bright light conditions and to see color. We as humans have three types of cones for short, medium, and long wavelength light. So when light enters the eye through the pupil and passes through the lens it becomes focused on the back of the eyeball where the rods and cones are. The light that enters the eye is of specific wavelengths, which is what determines the color of the object that we can see. The visible light spectrum for the human eye is from about 390nm to 700nm, just beyond the spectrum lies ultraviolet light which is too short of a wavelength and infrared with is too large of a wavelength to process. The object itself actually determines which wavelength is reflected back to our eye.
When we look at an orange, all wavelengths of the visible spectrum are absorbed by the material except for the specific wavelengths that we process as orange, which are reflected back to our eyes. To simplify how it depends upon arrangement of electrons in the atoms of the material is that when light, which carries energy, strikes an object and some of it is absorbed and some is not depends upon the electron structure of the material. We see an orange as orange because the electrons in the atoms of the orange peel absorb all other wavelengths of the visible light except orange, which are reflected back to the eye. Once the orange wavelengths reach the eye, the cones that correspond to that wavelength are then stimulated to a certain degree and then that information is passed to the optic nerve to the brain to be processed by the visual cortex into the “color” orange that we perceive.
While we are much better at distinguishing varying colors and degrees of color than most mammals, some creatures have four types of cones that allow them to see parts of the light spectrum we are unable to. Some insects, birds and fish have been found to see some degrees of ultraviolet light, which have too short of wavelengths for us to see.
How many colors can the human eye see? Despite not being at the top of the evolutionary vision chain, humans are still able to see and process quite a range of color.