Amity polishes a red apple in a bright kitchen. The apple looks red, the towel looks yellow, the counter looks white.
The kitchen's light is the same white light everywhere. So why does each surface show a different color? The answer is a sorting that happens at the surface.
White light is a mixture of all the wavelengths of visible light, and that whole mixture arrives at every surface in the kitchen.
At the apple's skin, the mixture is sorted. The skin reflects the red wavelengths, and it absorbs the rest.
Absorbed wavelengths end at the surface: they never reach your eye. Reflected wavelengths bounce away, and some of them reach your eye.
So out of everything that arrived, your eye receives only red from the apple. The apple looks red.
The apple makes no light of its own. It can only sort what arrives: reflect some wavelengths, absorb the others.
Two boundary cases complete the picture. A surface that reflects nearly all the arriving wavelengths looks white. A surface that reflects none of the arriving light looks black.
In earlier grades, you sorted what light does at a surface: reflected, absorbed, or transmitted. This lesson is that sort doing its day job, wavelength by wavelength.
Zeno's green lawn chair sits in white sunlight. Explain why it looks green.
White sunlight arrives carrying every visible wavelength.
The chair's surface reflects the green wavelengths and absorbs the rest.
Zeno's eye receives only the reflected green.
The chair looks green because only green wavelengths leave its surface and reach the eye.
Bard's bike tire looks black in the same sunlight. What is the tire's surface doing to the arriving light?
The full mixture arrives at the tire.
The tire's surface absorbs nearly all of it and reflects almost none.
A surface that reflects none of the arriving light looks black.
The tire absorbs nearly every arriving wavelength, so almost nothing reaches the eye and the tire looks black.
Ysolde's blue backpack sits in white light. Which wavelengths leave the backpack's surface and reach her eye?
Bard says: 'A yellow tennis ball's skin adds yellow color to the light it sends back.' Is Bard correct?
Ysolde says: 'You see a surface's color because your eye receives only the wavelengths the surface reflects.' Is Ysolde correct?
Zeno's orange basketball sits in white light. Why does it look orange?
A black hoodie sits in bright white light. What is its surface doing to the arriving visible wavelengths?
A black cap and a white cap sit side by side in the same white light. Which cap's surface absorbs the larger share of the arriving visible light?