Colour questions look tricky, but they all come down to one idea: you see an object’s colour because of the light it reflects into your eyes.
The two-question method
- What colour light is reaching the object?
- Can the object reflect that colour?
If yes, it looks that colour. If no, it absorbs the light and looks black.
Try it
- Blue shirt, red light: red light arrives, but the shirt only reflects blue. It looks black.
- White paper, red light: white reflects all colours, but only red arrives. It looks red.
- Red car through a green filter: the car reflects red, but the filter absorbs red. It looks black.
Filters
A filter transmits its own colour and absorbs the rest. White light through a red filter and then a blue filter gives no light at all: the red filter removes everything except red, and the blue filter absorbs the red.
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