What determines which light frequencies are reflected vs absorbed?

[Matrixman13]

I understand that what we perceive as color is really just certain frequencies of light that are reflected by objects. But what determines what frequencies are absorbed and which ones are reflected.

 

[chroot]

The chemical structure of the substance. Some atoms directly absorb certain frequencies of light, because their electron structures provide a transition with matching energy. Larger molecules have specific modes of vibration or rotation that can absorb frequencies or ranges of frequencies. Indeed, specific parts of large organic molecules are responsible for specific kinds of coloring.

Here's a good website to get you started:

http://www.chm.bris.ac.uk/webprojects2002/price/colour.htm

- Warren