When we stroll through a spring garden, red roses, yellow jasmine, and purple lilacs bloom in a riot of colors. It seems as if color is nature’s most generous gift. But have you ever wondered where these brilliant hues come from? In fact, the formation of color is an exquisite drama jointly performed by light, matter, and the visual system, with many interesting scientific principles hidden behind it.

To explore the mystery of color, we must first understand light. Light is essentially an electromagnetic wave, and the “visible light” we can see is just a small segment of the electromagnetic spectrum, with a wavelength range of approximately 400 nanometers (violet) to 700 nanometers (red). Just as the black and white keys on a piano can combine to create countless melodies, light of different wavelengths can also form thousands of colors.

The most common source of visible light is the sun. What appears to be pure white light is actually a “composite light” composed of a mixture of various monochromatic lights such as red, orange, yellow, green, blue, indigo, and violet. In the 17th century, Newton conducted a famous experiment with a prism: when sunlight passes through a prism, light of different wavelengths is separated due to different refraction angles, forming a spectrum like a rainbow. This discovery revealed an important fact: white light is a mixture of various colored lights.

Different wavelengths of light correspond to different colors perceived by the human eye: longer wavelengths (620-750 nanometers) allow us to see red and orange; medium wavelengths (520-570 nanometers) appear green; and shorter wavelengths (450-495 nanometers) appear blue and violet.

Light itself has no color. The colors of objects we see are the result of the “interaction” between matter and light. When light shines on an object, phenomena such as reflection, absorption, transmission, or scattering occur, and these processes together determine the color of the object.

For opaque objects such as leaves, flowers, and clothes, their colors are mainly determined by reflected light. The molecular structure of the object’s surface is like a “filter”, which selectively absorbs light of certain wavelengths while reflecting light of other wavelengths. The reflected light enters our eyes, forming the color we see.

For example, leaves are green because chlorophyll in the leaves particularly “likes” to absorb red and blue light but “keeps out” green light; red apples appear red because the pigments in their epidermal cells absorb short-wavelength light such as blue and green, and only reflect red light; black objects can absorb almost all wavelengths of light, with very little light reflected, so they look black; white objects, on the other hand, can reflect almost all wavelengths of light, thus appearing white.

Transparent or translucent objects, such as glass, water, and colored plastics, get their colors from transmitted light. When light passes through these objects, some wavelengths of light are absorbed, and the remaining light passes through the object into our eyes, allowing us to see a specific color.

For instance, blue glass allows blue light to pass through smoothly but absorbs light of other wavelengths, so we see it as blue; the ultraviolet disinfection lamps commonly used in hospitals have lampshades that absorb visible light and only allow ultraviolet light to transmit (although we cannot see ultraviolet light, the principle is similar).

Some colors are formed due to “scattering”. Scattering refers to the phenomenon where light is dispersed in all directions when it encounters tiny particles (such as molecules, water droplets, and dust in the air). Moreover, the degree of scattering is related to the wavelength of light; short-wavelength light (such as blue and violet light) is more easily scattered than long-wavelength light (such as red and orange light).

The sky is blue because blue light in sunlight is scattered in all directions by nitrogen and oxygen molecules in the air, so no matter which direction we look at the sky, a large amount of blue light enters our eyes. During sunrise or sunset, the path of sunlight through the atmosphere is longer, blue light is largely scattered, and the remaining red and orange light is more easily observed, so the sky appears a beautiful orange-red.

The sea appears blue, partly because it reflects the color of the sky, and partly because sea water molecules scatter blue light more strongly than light of other wavelengths.

Even if the interaction between light and matter forms light of a specific wavelength, our ability to “see” color ultimately depends on our visual system. There are two types of photoreceptor cells on the retina of the human eye: rod cells and cone cells. Rod cells are mainly responsible for perceiving light and dark, while cone cells are responsible for perceiving color.

There are three types of cone cells, each most sensitive to light of three wavelengths: red, green, and blue, known as “trichromatic receptors”. When light of different wavelengths enters the eye, these three types of cone cells are stimulated to varying degrees, generating nerve signals. These signals are transmitted to the visual center of the brain through the optic nerve, and after integration and processing by the brain, they form our perception of color.

For example, when red and green light enter the eye at the same time, the brain interprets it as “yellow”; when red, green, and blue light are mixed in a certain proportion, the brain perceives it as “white”. The color TVs and computer monitors we usually see use this principle – by mixing red, green, and blue primary colors of light to simulate various colors in nature.

It is worth mentioning that color perception is somewhat subjective. Each person’s cone cell sensitivity may vary, which leads to some people having “color blindness” or “color weakness”. They cannot accurately distinguish certain colors; for example, people with red-green color blindness have difficulty distinguishing between red and green.

In addition, the intensity of light and the color of the surrounding environment (i.e., the “background color”) can also affect our judgment of color. For example, the same piece of clothing may look different in sunlight and under light, which is the influence of the environment on color perception.

The formation of color is a wonderful process: from light sources such as the sun emitting visible light containing various wavelengths, to objects “filtering” out light of specific wavelengths through reflection, absorption, transmission, or scattering, to this light being perceived by the human visual system and transmitted to the brain, ultimately forming the colors we see.

Color not only enriches our visual world but also plays an important role in our lives – it affects our emotions (for example, red makes people feel enthusiastic, blue makes people feel calm), judgments, and behaviors. Understanding the principles of color formation allows us to more deeply appreciate this colorful world and better use color to beautify our lives and improve work efficiency.

Next time you see a beautiful rainbow, a clear blue sky, or bright flowers, think about the wonderful collaboration between light, matter, and the visual system behind them. I believe you will have a new understanding and feeling of these colors.