Color is a perception created by the interaction of light, matter, and the observer’s brain, not an inherent property of an object. When light strikes a surface, some wavelengths are absorbed, and others are reflected or transmitted to our eyes. The difference in which wavelengths are returned generates the sensation of color.
The Physics of Visible Light
Light travels in waves, and the distance between two peaks is the wavelength. The human eye detects visible light, a small segment of the electromagnetic spectrum spanning 380 to 750 nanometers. Different wavelengths within this band correspond to the colors we see, from violet (short) to red (long).
White light, like sunlight, contains all visible wavelengths combined. When light hits an object, the molecular structure determines which wavelengths are absorbed and which are reflected. For example, a blue shirt absorbs red and green wavelengths while reflecting only blue. The reflected wavelengths dictate the color we perceive.
Color Production Through Subtraction (Pigments)
The color of physical objects like paints, dyes, and inks is created through subtractive mixing, relying on chemical pigments. These pigments function by selectively absorbing, or “subtracting,” specific parts of the visible light spectrum. The observed color is the remaining light that the pigment reflects.
The primary colors for this model are Cyan, Magenta, and Yellow (CMY). For instance, a magenta pigment absorbs green light, reflecting red and blue wavelengths. Mixing two subtractive primaries results in a darker color because each pigment absorbs a different set of wavelengths, reducing the light reflected.
When all three subtractive primaries are mixed in equal measure, they ideally absorb nearly all incoming light. This absence of reflected light is perceived as black. In practical printing, Black (K) is added, creating CMYK, to achieve a richer black and conserve colored inks.
Color Production Through Addition (Light Sources)
Color created by emitted light, such as from computer screens and stage lighting, uses additive mixing. This process starts with darkness and builds color by combining different wavelengths of light directly. The primary colors in this model are Red, Green, and Blue (RGB), which are the fundamental colors to which human vision is most sensitive. By varying the intensity of these three light sources, millions of colors can be produced.
Combining Additive Primaries
Combining red light and green light creates yellow. Mixing red light and blue light yields magenta, and green light with blue light produces cyan. The combination of all three additive primary colors at maximum intensity results in the presence of all visible wavelengths. This full combination of light is perceived as white light. This outcome contrasts with the subtractive model, where mixing all primaries results in black.
How the Human Eye Interprets Color
Light waves must be translated into electrical signals before the brain can process them as color. Light enters the eye and is focused onto the retina, a layer of light-sensitive cells containing specialized photoreceptor cells called cones. Cones are responsible for color vision.
Most humans possess three types of cone cells, known as trichromacy. Each cone type contains a different photopigment and is maximally sensitive to specific wavelengths: one responds to long wavelengths (red), another to medium (green), and a third to short (blue). Color perception occurs when incoming light stimulates these three cone types to varying degrees.
The combined signals are transmitted along the optic nerve to the visual cortex in the brain. The brain processes these electrical signals, interpreting the ratio of stimulation from the cones to construct the final sensation of color. This allows us to distinguish an estimated one million different colors.