Color is what we see when light reaches our eyes. Sunlight looks white, but it holds all the colors of the rainbow. Isaac Newton showed this with prisms and described his experiments in Opticks (1704).
A surface absorbs some of the light that falls on it and reflects the rest. We see the reflected part. A ripe tomato absorbs most colors and reflects mostly red, so it looks red. A white sheet reflects nearly all the light; a black coat absorbs nearly all of it.
Key idea
An object's color depends on the light that falls on it and what its surface reflects. Artists describe any color with three properties: hue, value and saturation.
Why it works
Change the light and you change what can be reflected. Under pure blue light a red tomato has almost no red light to reflect, so it looks very dark. Under a red stage light, a white shirt reflects the red and looks red. Our eyes do adjust to ordinary light changes (a white page looks white under a lamp and in daylight), which is why we rarely notice. Scientists call that adjustment color constancy.
| Property | The question it answers | Example |
|---|---|---|
| Hue | Which color family? | red, blue-green |
| Value | How light or dark? | pale pink is light; maroon is dark |
| Saturation | How pure or grayed? | fire-engine red is pure; brick red is grayed |
Worked example: Color under colored light
A white shirt is lit only by a red stage light. What color does it look?
- White reflects nearly every color of light that reaches it.
- Only red light reaches it.
- So it reflects red and looks red.
Answer: Red.
Common mistake
Thinking an object keeps its color in any light. Its color is a partnership between the light and the surface. Painters who work outdoors see this every day: a white house looks golden at sunset and bluish at dusk.