I only had physics in college for 2 years, so I am not exactly an expert. I am wondering why some things have a certain colour. My idea goes like this:

Let's say there is a red wall. I think, light impinges on the wall. At an atomic level, I suppose we can think of light as photons. A photon interacts with an an electron from the pigment molecules. The electron absorbs some or all of the photon's energy. The electron with more energy goes up an 'orbit'. But at normal temperatures, this is not a stable situation, so it jumps back and gives off a photon. I suppose quantum constraints dictate that this photon has a very specific energy. The result is, we see red light, because of the nature of the pigment molecules and the energy of the photon emitted.

Does that describe the situation at all?

Is there only one 'red' or a spectrum of reds? I think, red light has a wavelength of about 400 nm. Do all wavelengths actually exist, as a continuous spectrum, or would the next possible wavelength be say 400 + x nm, where x is a quantum jump, so to speak? Would that still be 'red'?

And if the wall is black? Is it radiating back in a, for us, non-visible wavelength?

A lot of related questions, I know. Thanks for any answers, this is puzzling me!