Question

How do we see color? Explain with at least 2 examples

Answer 1

Short answer: We see color because light of different wavelengths enters the eye, is filtered and absorbed by three types of cone photoreceptors (each tuned to different wavelength ranges), and the retina and brain compare the cones’ signals to compute chromatic information. Color is a brain interpretation of the pattern of activity across those cones, not a property solely of light or objects.

Step-by-step mechanism
1. Light from a source (sun, lamp) contains many wavelengths.
2. That light hits an object; the object’s surface absorbs some wavelengths and reflects or transmits others. The reflected light’s spectral composition reaches your eye.
3. In the retina, three kinds of cone cells (S, M, L — roughly short/blue, medium/green, long/red sensitivity) absorb photons with different efficiency across the spectrum. Rods are more sensitive in dim light but don’t contribute to color.
4. The brain compares the relative responses of the three cone types (for example: more L and M activity, less S) and converts those ratios into the perception of a particular hue, saturation and brightness. Later visual processing uses “opponent” channels (red vs green, blue vs yellow, light vs dark) to refine color signals and support color constancy.

Two clear examples

Example 1 — Why a banana looks yellow
- White light hitting the banana contains all visible wavelengths.
- Banana peel pigments absorb short/blue and some long/red wavelengths but strongly reflect wavelengths around the middle of the visible spectrum (roughly 570 nm).
- That reflected spectrum stimulates the L and M cones more than S cones; the brain interprets that cone-activity pattern as “yellow.”

Example 2 — Mixing colored light vs mixing paints
- Additive mixing (lights): When you shine red and green spotlights together on a white wall, the wall appears yellow because red light stimulates L cones, green stimulates M cones; combined activity matches the cone response pattern the brain interprets as yellow. This is why RGB pixels on a screen can produce many colors.
- Subtractive mixing (pigments/paints): A blue paint absorbs long (red) and some medium (green) wavelengths and reflects short (blue); yellow paint absorbs short wavelengths and reflects medium/long. When you mix blue and yellow paint, each pigment removes (absorbs) different parts of the spectrum so the light reflected from the mixture is mostly the wavelengths they both let through (often greenish), so the mixture appears green. This works by filtering light rather than by adding emitted light.

Bonus useful points (brief)
- Color blindness (e.g., red-green deficiency) usually comes from missing or shifted cone pigments; two people can look at the same object and report different colors because their cone responses differ.
- Metamerism: Two different spectral compositions can produce the same cone responses and therefore look identical in color (e.g., a certain LED and sunlight might both look “warm white” despite having different spectra).
- In low light (scotopic vision) rods dominate and color vision is poor or absent.

If you want, I can show simple spectra diagrams, give numerical sensitivity peaks for human cones, or simulate how different spectra produce particular cone responses. Which would you like?