Colors are a fundamental part of our visual experience and perception of the world. But where do colors actually come from? How and why do we see certain colors? The answers lie in the physics and biology of how light, objects, and our eyes interact. By understanding some key principles of optics, chemistry, and neuroscience, we can gain insight into the fascinating science behind how we perceive color.
The Physics of Color
At the most basic level, color comes from light. Sunlight appears white to our eyes. But as Isaac Newton demonstrated with his famous prism experiments in the 1660s, white light is actually composed of a rainbow of colors mixed together. When white light passes through a prism, the different wavelengths separate because of differences in refraction. The visible spectrum of light that humans can see ranges from violet and blue light at shorter wavelengths to red light at longer wavelengths.
The color of an object depends on what wavelengths of light it absorbs and reflects. When all visible wavelengths are reflected equally, we see white. When certain wavelengths are absorbed more than others, we see color. For example, a red apple absorbs most of the spectrum and reflects predominantly long red wavelengths. A blue balloon absorbs all colors except blue.
| Color | Wavelength range (nm) |
|---|---|
| Red | 620-750 |
| Orange | 590-620 |
| Yellow | 570-590 |
| Green | 495-570 |
| Blue | 450-495 |
| Violet | 380-450 |
The wavelength ranges corresponding to different colors in the visible spectrum.
The absorption and reflection of light is influenced by the chemical composition of materials. Pigments in paints and dyes contain colored compounds that preferentially absorb certain wavelengths. The color we perceive is the complement of the color absorbed. For example, chlorophyll in plants absorbs red and blue light, causing predominant green reflection that makes leaves appear green.
Color Perception in the Eye and Brain
Seeing color requires both physics of light and the biology of vision. The retina at the back of our eyes contains photoreceptor cells called rods and cones. Rods are sensitive to brightness but not color. Cones are specialized into different types that are sensitive to red, blue, or green wavelengths. Signals from these cones converge and get processed in the visual cortex of our brain.
Remarkably, our perception of millions of colors depends on the relative activity between just three cone types. Differences in wavelength sensitivity and neural processing create all the colors we experience. For example, yellow light strongly stimulates both the red and green cones. Violet light stimulates the blue cone more than the red. White stimulates all three cone types roughly equally.
Artists mix paints of different hues to create new colors. Televisions and computer screens produce color by combining dots of red, green, and blue light. Our visual system integrates those components into the smooth, seamless colors we perceive.
The distribution and density of cone cells also affects color vision. Having more cones sensitive to certain wavelengths can expand our ability to discriminate similar hues in that range. Many animals have very different cone compositions and sensitivities, so they see the world in dramatically different colors than we do!
Color Deficiency and Illusions
Our color perception can change in various ways. Color blindness or deficiency occurs when one or more cone cell types are absent or not functioning properly. Red-green color deficiency is most common, making it hard to distinguish reds, greens, and related hues. Other visual disorders may also affect color perception.
Optical illusions can trick our eyes and brain into seeing false or distorted colors. Contrast effects, afterimages, and adaptation influence how color signals get processed in the visual system. Clever illusions reveal the complexity behind our subjective experience of color.
Conclusion
Color deeply impacts how we perceive and interact with the world. But color itself arises from a fascinating interplay of light physics, material properties, and biological processing. Gaining insight into the underlying mechanisms of color enriches our appreciation for the colorful beauty all around us. From physics, to eyes, to brains, the science of color perception continues enlightening our visual world.