Color

Color, or colour in Commonwealth English, is how we see the world around us through our eyes. It happens when light activates special cells called cone cells in our eyes. Even though color isn’t a part of objects themselves, we see color because of how objects absorb, emit, reflect, and transmit light. Most humans can see colors because of three types of cone cells, but other animals, like bees, can see different colors, such as ultraviolet light, because their eyes are sensitive to different wavelengths.

Colors have properties like hue, colorfulness, and lightness. We can mix colors in two main ways: by adding light together (additive mixing) or by mixing pigments (subtractive mixing). Because of a phenomenon called metamerism, two different colors can look the same when mixed in the right amounts. To help organize and reproduce colors accurately, we use color spaces and color models such as RGB, CMYK, HSL/HSV, CIE Lab, and YCbCr/YUV. These tools are important for color reproduction in print, photography, computer monitors, and television.

Colors play a big role in our emotions, activities, and even our sense of nationality. Different cultures may name color regions differently, and sometimes these areas overlap. In art, color theory helps artists use colors in pleasing and harmonious ways. This theory includes ideas about color complements, color balance, and the classification of primary, secondary, and tertiary colors. The study of all things related to color is called color science.

Physical properties

Electromagnetic radiation has a special length and strength. When this length is inside the visible spectrum (the range of lengths humans can see, about from 390 nm to 700 nm), it is called "visible light".

Most light sources give out light at many different lengths. The way these lengths mix decides the color we see. Even though many mixes can make the same color, each mix is called a metamer of that color.

Spectral colors

Main article: Spectral color

The colors we see in a rainbow—like red, orange, yellow, green, blue, indigo, and violet—were named by Isaac Newton in 1671. These are made by single lengths of visible light and are very strong or "pure". Any color can be made by mixing these rainbow colors together.

These rainbow colors blend smoothly into each other, and different cultures may name them a bit differently. The way we split them into names can change, especially for indigo and cyan. How bright a rainbow color is can change how we see it. For example, a dim orange-yellow looks brown, and a dim yellow-green looks olive green. When rainbow light gets brighter, its color can shift toward yellow or blue.

Color of objects

An object's color comes from how it takes in and sends out light. Most objects send out some light but don’t act like glasses or mirrors. A transparent object lets almost all light pass through, so it looks colorless. An opaque object doesn’t let light through and instead takes in or sends out the light it gets. Like transparent objects, translucent objects let some light through but look colored because they mix or take in some lengths of light inside, often turning that light into heat.

Color vision

People have known about light and how we see color for a long time. But it was Isaac Newton who showed that light is what gives us the sensation of color. Later, Johann Wolfgang von Goethe wrote a book about how we experience color.

Thomas Young came up with an idea that our eyes have three types of cells that help us see different colors. This idea was proven true later by James Clerk Maxwell and Hermann von Helmholtz. They showed that any color we see is made by mixing three basic colors.

Our eyes can tell colors apart because of special cells called cones in our retina. There are three types of these cones. One type is best at seeing blue light. The other two types are best at seeing green and yellow light.

When light enters our eyes, it makes these three types of cones react. How much each type reacts tells our brain what color we are seeing. Together, these reactions let us see about ten million different colors.

After the cones react to light, the information goes to different parts of the brain. There, it is organized into three groups: red-green, blue-yellow, and black-white. This helps us understand colors better and explains why we can’t see colors like “reddish green” or “yellowish blue”.

Some people have trouble seeing colors the way most people do. This is called color vision deficiency. It can be mild, meaning they see fewer shades, or more severe, meaning they can’t see some colors at all. The most common type makes it hard to tell red from green.

Main article: Tetrachromacy

Most humans see colors with three types of cones, but some women may have four types. This could let them see many more colors than others can, though this is not common.

Main article: Synesthesia

Some people see colors when they hear sounds or see letters and numbers. This is called synesthesia. It is a special way their brain connects different senses.

Main article: Afterimage

If you look at a bright color for a while and then look away, you might still see that color, but in a different shade. This is called an afterimage. Artists sometimes use this effect in their work.

Our eyes adjust to different lighting so that colors appear the same. For example, a red apple looks red whether it is in sunlight or indoor light. This helps us recognize objects no matter where they are.

Reproduction

Color reproduction is the science of making colors that look just like the color we want. It helps us create the right mix of light to show a certain color. Many colors are mixes of different light wavelengths, not single colors. These mixed colors are often described by their main wavelength, which is like the closest single color to what we see.

Some colors, like black, gray, white, pink, tan, and magenta, can't be made with just one color of light. Two different mixes of light that affect our eyes the same way will look like the same color. This is called being metamers. For example, the white light from a fluorescent lamp and daylight may look the same, even though their light mixes are different.

Most colors we see can be made by mixing three main colors. This is used in photos, printing, TV, and more. While we can’t make a color exactly like the purest form, we can get very close. The range of colors a system can make is called its gamut. Different devices see color differently, so careful management is needed to keep colors looking right when they are saved or shown on screens.

Additive coloring

Additive color is when we mix light of different colors together. Red, green, and blue are the main colors used in systems like projectors, TVs, and computer screens.

Subtractive coloring

Subtractive coloring uses dyes, inks, pigments, or filters to take away some colors of light and keep others. The color we see on a surface is the light that isn’t taken away. Without any dyes or paints, materials usually show all colors of light. When we add dye or paint, it takes away some colors, so we see the remaining color. For example, red paint looks red because it only lets red light show. If we shine blue light on red paint, it may look black because the blue light is taken away.

Structural color

Further information: Structural coloration and Animal coloration

Structural colors come from how light interacts with tiny patterns in materials, not from pigments. When a material has very fine lines or layers, it can create colorful effects by bending and scattering light. For example, the blue sky appears blue because tiny air particles scatter shorter blue light more. Similar effects make opals shine and give human eyes their blue color.

When these patterns are arranged in very specific ways, like the tiny lines on a CD, they can split white light into its many colors, similar to how a rainbow forms. This is why some butterfly wings, bird feathers like those of a blue jay, and even soap bubbles look blue or green. The color you see can change depending on the angle you look from, creating a shiny, shifting effect like that seen in peacock feathers or mother of pearl. Scientists have studied these effects for centuries, and today they help create special products like certain cosmetics.

Optimal colors

Main article: Gamut § Surfaces (optimal colors)

Optimal colors are the brightest and most intense colors that objects can show. These colors are the limit of what we can see in objects, though we cannot make real objects with these colors using today’s technology.

These special colors form a shape in color spaces called the optimal color solid. The way colors reflect light decides if they can be optimal colors. With today’s technology, we cannot create materials that match these perfect colors.

There are four main types of these optimal color patterns. Some look like the colors we see in rainbows, while others give us deep purple or blue colors. In these special color shapes, the colors of the rainbow appear dark, even though they are very pure in a scientific way.

In color science, these optimal colors create sharp edges from dark to light colors, like moving from black to red, orange, yellow, and white, or from black to deep blue, cyan, and white. Computers can now calculate these perfect color shapes very quickly.

Cultural perspective

Colors have special meanings in different cultures and can affect how people feel and act. Artists, writers, and even restaurants use colors to create certain feelings or effects. For example, the color red can affect how well people think, and the colors red and yellow together can make people feel hungry.

Colors also help us remember things better. A color photo is usually easier to remember than a black-and-white photo. Wearing bright colors can make you more noticeable to others.

See also: Lists of colors and Web colors

Colors can be different in many ways, such as their hue (like red, orange, or blue), how strong they are (saturation), and how bright or dark they are (brightness). Some color names come from objects, like the fruit "orange," while others are more general, like "red." Studies have shown that all languages start by distinguishing dark colors from bright ones, then add names for red, yellow, or green, and later include more colors like blue and purple.