For exaple when you put a piece of red plastic in front of a flashlight how can the wavelengths just change?
In: Physics
It generally doesn’t. The colour red bounces, others don’t. That’s what makes it red. White(ish) light from a flashlight contains all the individual colours of the rainbow in it all mixed together. [A prism breaks up those mixed up colours](https://www.science-sparks.com/rainbow-with-a-prism/) – it doesn’t make colours, just separates them.
If you shine a green or blue light at a red object, it will appear black, or very nearly so since blue is mostly absorbed by a red objective. It might be a tiny bit visible but the majority of that light is absorbed, not reflected.
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