How objects reflect green light?

Question

I'm currently interested in energy levels and I've learned that there are energy gaps between molecular orbitals that makes things appear transparent (for visible light).

Thus, objects like glass can still absorb light with higher frequencies, which cannot pass those gaps.

But can someone please explain me how other objects (like chloroplasts inside leaves) can absorb (i.e., not being transparent) both low- and high-frequency lights (less than ~400 nm and more than ~600 nm per say), but reflect mid-frequency light, like green (~500 nm) - ?

I'm basically searching for specific keywords\sources for further reading.

Answer 1

Bandgap insulators have colors that are determined mostly by one parameter, the size of the band gap between occupied and unoccupied states.

Molecules are different. Pigments have electronic transitions between different levels, and there can be different pairs of levels with strong absorption.

There are simple inorganic pigments, like transition metals or color centers (things that a physicist understands). See for example this page about emerald: http://www.webexhibits.org/causesofcolor/6AB.html

Chlorophyll is more complicated.