Well.. no color “exists”, they are just wave like particles.. not even “reality” as we see it exists.. it’s just in our minds..
I think that what they really mean is that there is no wavelength for the purple we see
Except for colors that are combinations of different, disconnected, wavelengths. This is why there are red and blue stars, but no green or magenta stars.
That's not really the reason. Green is a spectral color, and in fact the sun peaks around the green part of the spectrum. But to see a star as green, it would need to exclusively emit green light.
