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.

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). 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. In art, color theory helps artists use colors in pleasing 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.

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 color for a long time. Isaac Newton showed that light gives us the sensation of color. Later, Johann Wolfgang von Goethe wrote a book about how we experience color.

Thomas Young suggested that our eyes have three types of cells that help us see color. This was proven true by James Clerk Maxwell and Hermann von Helmholtz. They showed that any color 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 cones. One type sees blue best. The other two see green and yellow best.

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

After the cones react, the information goes to different parts of the brain. It is organized into three groups: red-green, blue-yellow, and black-white. This helps us understand colors better.

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 more colors than others, 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 look just like the color we want. It helps us mix the right light to show a certain color. Many colors are mixes of different light, not single colors. These mixed colors are often described by their main wavelength.

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 look the same to our eyes are called 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. The range of colors a system can make is called its gamut. Different devices see color differently, so we need to manage colors carefully to keep them looking right 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. 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 happen when light meets tiny patterns in materials. These patterns are not pigments but very fine lines or layers that bend and scatter light. For example, the sky looks blue because tiny air particles scatter blue light more than other colors. Similar effects make opals sparkle and give human eyes their blue color.

When these patterns are arranged in special ways, like the lines on a CD, they can split white light into many colors, like a rainbow. 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 a long time, and they help make special products like some 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, but 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 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. Artists, writers, and even restaurants use colors to create certain feelings. For example, the color red can change how people think, and 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, 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." 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.