Spectral emission by elements occurs in discrete wavelengths. There are only about 118 elements. My question is whether there are pure colors either disfavored in nature, or even disallowed?
The sun (via prism) appears to generate a continuum of visible frequencies, but of course that would probably appear to be the case because the eye would mix adjacent spectral colors and the resultant (near-spectral) color would seem to fill in the gap (note: that is a question, not a statement).
It is often recited that "black bodies" (like the sun) emit a spectrum of radiation, but how would we notice small discontinuities, if they existed?
Red-shift might create visible frequencies that otherwise do not occur. But do we have some basis other than (prism + visual intuition) that all pure visible frequencies do in fact correspond to some possible natural or artificial source?
Apologies for the naivete of the question, if that is the case, and the likelihood that the answer may not have much practical significance. There were related question on the site and on Google but nothing directly on point.