When we see colors, it is because certain wavelengths of light are reflected off an object while other wavelengths are absorbed. The wavelengths that are reflected determine what color our eyes perceive. For example, a red object appears red because it reflects wavelengths of light in the red part of the visible spectrum, while absorbing other wavelengths. Understanding how color reflection works helps explain phenomena like why the sky is blue and how objects have their particular colors.
How Light and Color Work
Visible light consists of a spectrum of wavelengths that range from short to long, corresponding to the colors violet, indigo, blue, green, yellow, orange and red. When white light, which contains all wavelengths, shines on an object, some of the wavelengths are absorbed while others are reflected.
The reflected wavelengths are what our eyes see as the object’s color. For example, a banana appears yellow because it reflects light in the yellow wavelengths while absorbing other colors. A stop sign looks red because it reflects the long wavelengths we see as red and absorbs shorter bluish wavelengths.
The absorbed colors are essentially subtracted from the white light, while the reflected colors add up to the object’s visible hue. So if an object reflects mostly red and green wavelengths, we will see it as yellow since red and green light combine to produce that color.
Why the Sky is Blue
The sky appears blue during the day because molecules in the atmosphere scatter blue wavelengths more than other colors. Shorter wavelength light is more prone to scattering than longer wavelengths.
When sunlight enters the atmosphere, light from the violet and blue end of the spectrum is scattered in all directions by gas molecules and airborne particles. The scattered blue light reaches our eyes, making the sky look blue from the ground. At sunrise and sunset, the sun’s light has to pass through more atmosphere and scattering to reach us, allowing more red light through and causing dramatic orange and red hues.
Absorption vs Reflection
When light strikes an object, two things can happen: some wavelengths are absorbed and others are reflected. The reflected wavelengths determine the color we see. But why do different materials absorb and reflect different wavelengths?
The answer lies in the atomic and molecular structure of materials. Factors like electron configuration, chemical bonds, and band gaps in metals, dyes, and pigments cause them to preferentially absorb or transmit certain wavelengths. Materials containing certain transition metals, for example, absorb frequencies that cancel out yellow light, causing an object to appear blue or purple instead.
Understanding these absorption mechanisms allowed scientists to create theories of color that helped pioneer modern chemistry and quantum mechanics.
How Pigments and Dyes Produce Color
Pigments are chemicals that selectively absorb certain wavelengths of light. By absorbing some colors more than others, they leave the reflected colors to be seen as the pigment’s color. Common pigments include melanin in skin and hair, chlorophyll in plants, and hemoglobin in blood.
Dyes are similar but are usually soluble chemicals rather than insoluble powders. Fabric dyes work by attaching to fabric fibers and absorbing some colors while reflecting others back to the eye. Mixing multiple dyes expands the range of possible colors.
Both pigments and dyes appear a certain color because their molecular structures absorb specific wavelengths while reflecting or transmitting others. Modern chemistry allows designing molecules to absorb precisely the desired colors.
Structural Color in Nature
While pigments and dyes produce color through absorption, some colors in nature come from light interacting with complex nanostructures rather than chemicals. These include iridescent butterflies, feathers, seashells, and opals.
Their minute structures cause light waves to interfere and reflect specific colors through diffraction effects. Small changes in the viewing angle can dramatically shift the color. This structural color relies on physics rather than chemistry, creating vivid optical effects without any pigments.
Fluorescence and Phosphorescence
Some substances absorb light energy and re-emit it as different colors through fluorescence or phosphorescence. Fluorescent materials absorb and re-radiate light quickly, while phosphorescent ones have longer-lasting glows.
Posters, paints, and laundry detergents often contain fluorescent dyes. Glow-in-the-dark toys and watches use phosphorescent materials. These absorbing and re-emitting processes result in dramatic color changes compared to regular reflected light.
Metamerism and Color Constancy
Metamerism describes when two colors match under some light sources but not others. It occurs because the spectral power distributions of different illuminants, like daylight versus indoor lighting, differ substantially. A color that reflects a lot of yellowish wavelengths under daylight might appear more orange under tungsten lights.
Fortunately, our brains process colors subjectively through color constancy. This helps a color seem relatively constant under various lighting conditions, an important adaptation that provides visual continuity in our complex environments.
Color Mixing Principles
Combining certain primary pigment colors results in additive mixtures that reflect a new color wavelength. For pigments, the common primaries are cyan, magenta and yellow. Mixing cyan and magenta makes blue, combining cyan and yellow creates green, and mixing magenta and yellow results in red.
Light mixes additively too, but uses different primaries: red, green and blue. Televisions and computer screens create a wide gamut of colors by combining varying intensities of red, green and blue light.
In subtractive color mixing, combining paint pigments produces darker colors. This underlies four-color printing using cyan, magenta, yellow and black inks to create color images and graphics.
Color in Art and Design
Understanding the science of color reflection allows artists and designers to create desired visual effects. In painting, reflected colors combine based on the types of pigments used. Digital design relies on manipulating light wavelengths using RGB color models.
Color theory principles help choose colors that evoke particular moods or convey visual impact. The reflective properties of metals, minerals and dyes produced the first artistic palettes, while modern technologies have enabled creating any imaginable color.
Conclusion
An object’s perceived color comes from the wavelengths of light it reflects to our eyes. Absorption and reflection of specific frequencies determine a material’s color. Knowledge of light physics, dye chemistry and nanostructures gives insight into color creation and the mechanisms behind vivid natural optical effects. Whether using pigments, particles or pixels, the nuanced interplay of reflection, absorption and emission enables an infinite array of possible colors.
