Good question! What your teacher said is basically correct. Light from the sun contains all the colors in it. Plants look green because the chloroplasts in the plant cells absorb red and blue light to make the energy. The color that is left over - green - gets reflected instead of absorbed and that is what you see. Most things get their color that way: that is by absorbing certain colors of light and reflecting the rest.
Iridescent colors come from something called "interference" which I won't explain here. This usually occurs for thin films like soap bubbles, oils on water, insect wings, etc. This phenomenon *is* a kind of reflection - but only certain colors get reflected. The color reflected has to do with the distance the light travels to get through the film so if you see it from an angle, it looks like a slightly different color because the light that reaches your eye travels through the film at an angle too. Since it is going through at an angle, it has to travel a longer distance inside the film. There are also paints that do this: they are made up of lots of little thin flakes which act like thin films of oil.
There are other ways for things to get their colors other than reflection, you know. One way is scattering. In scattering, light of a certain color bounces from molecule to molecule instead of transmitting directly through the material. Materials that have this property end up looking like they are glowing because the scattered light looks like it is coming from everywhere inside the material. A good example of this is air, which has a slightly bluish glow. If you don't believe me, look up on a sunny day! The sky is blue because it scatters blue light coming from the sun. At sunset, when the sun's light travels through the most atmosphere, it appears red because most of the bluer light has been scattered by the air.
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