How the Eye Perceives Color
The color you see is simply a reflection.
Light
Color is visible light and light exists in different wavelengths. These wavelengths are forms of electromagnetic radiation and represent different types of light. As in nearly all radiation, light does not hold a physical shape, meaning that it can pass through or be absorbed by objects.
Light waves also travel on their own, without the help of any other type of matter (unlike sound or water waves). This means that light is a completely independent force and can travel anywhere, even through the vacuum of space.
Light also creates the color spectrum. The visible color spectrum is seen when light goes through a prism. This separates out each color found within light into twelve visible colors. There are eight main colors within these twelve, which are the ones that have their own wavelengths. The four remaining colors can be distinguished, but reside within a main colors wavelength boundaries.
Color
The color spectrum also exists without the help of prisms. Prisms simply allow us to see all the colors at once. As white visible light wavelengths naturally come in contact with matter, the matter (depending on it’s type) absorbs a certain amount of light. What isn’t absorbed is reflected back and is known as a color.
An object always absorbs as much light as it can. So, when someone sees something that’s red, it means the object has absorbed every other wavelength of light and has reflected back only that red wavelength. When something is white, it means that all of the wavelengths were absorbed, and when something is black all of the wavelengths were reflected.
Photoreceptor cells
Once the radiation is reflected and comes into vision, it’s funneled through photoreceptors in your retina. There are two types of photoreceptors: rods and cones. Rods see shades of gray, and cones are the only receptors that deal with seeing color. This is because there’s a pigment within the cones that allow that receptor to interpret the color in a way the brain can understand.
Since there are many cone receptors, each receptor falls into one of these three categories: the kind that has red pigment and takes red light — which is the majority of receptors in the human eye —the kind that takes green light, and then blue light — which makes up only about 2% of the total receptors in your eye.
As the photoreceptors process this light, they categorize how much of each type is present in the radiation. How much of each color is present is then added together to form the color within your head.
The difference in cone quantity between the types is significant, as it controls how much of each type of color we clearly see. When someone has bad vision, it’s always the color blue that goes blurry first, as there are less cones, and red is the last color to become hard to see.
Color blindness
When someone is color blind, it means that 1 or more of their cones is without pigment and they cannot see that color.
Scientists believe that early humans actually couldn’t see color. As mentioned in a previous article (“Origins of Color”), the first real use of blue pigment wasn’t until the ancient Egyptians. While there are many records of color blindness, a popular example of this is how in The Odyssey the ocean was referred to as a “wine-red sea”, which turned out to be an early description of blue before the color could fully be seen by the human eye. In this case, colorblindness was caused simply because blue receptor pigment had sadly not developed in humans yet.
Because some, or all, of the cones in someone who is colorblind are without pigment, it means that cones see things with less color or in black and white, as their rods still see in shades of gray.
Afterimages
Afterimages are a visual curiosity. One of the most popular types of afterimages are negative afterimages. These occur when you stare at a color for a long period of time and then look at a white surface. As you look at the surface, such as a wall, an imprint of what you were looking at before will be present in your vision. Except, the original color of the object will not be present: the complimentary color of the original one is in it’s place.
An example of this is something you can try on your own, given that you are able to. If you stare at the black dot in the center of the photo on the left for an extended period of time (such as a minute) and then look at a white surface, a green afterimage should appear on the surface.
The Cause
After looking at a particular, brightly color object, your eye’s photoreceptors become fatigued. When you then look at the white surface, the afterimage is still in your brain, but your eyes subtract the original color (in this instance pink) due to the fatigue. Once this happens the complimentary color takes the other’s place.
Conclusion
While this is only a basic description of some of the ways the eye perceives color, it’s incredibly important. All knowledge is better received with background context, and hopefully this take on the optical science of color is insightful to the realm of color and the human body.
