An apple is red because (I've been told) it absorbs all colors except for red, which it reflects. Quantum mechanically, this would translate to: molecules in its skin absorb a spectrum of wavelengths, but spontaneously emit a different spectrum of wavelengths which is dominated by red.
So why would the absorption spectrum be different from the emission spectrum, if they both come from electronic transition levels?
(Feel free to stop me here if my question doesn't make sense, I'm ignorant about this)
I've heard the answer that the absorption spectrum accommodates much more light than the emission spectrum because the former is affected by (e.g.) thermal fluctations whereas the latter is more tightly limited to electronic transitions.
If that's the case, shouldn't an ultracold apple stop being red? Do ultracold objects have colors?
I would guess not, as now the absorption spectrum = the emission spectrum.