would you care to enlighten me, so the speak, with an objective definition of green that covers all cases in which people call something green in color?
Whether or not it's possible to give an objective, covering-all-cases definition of a range of experiential qualia -- or even of one such quale -- doesn't really address the question whether such qualia are universals. If that specific shade of green can recur identically in more than one context, it's a universal in the sense in which ontologists use the word. If not -- that is, if two occurrences of what seem to be the exact same color are really two different but 'exactly similar' qualia -- then that specific shade is not a universal. (Most modern nominalists would invoke trope theory or something equivalent at that point.)
Perhaps I can give a concrete example.
It is possible to construct a set of color patches using different pigments, so that people with "normal" vision will say that two patches are identical, but people with color deficiencies will see them as different. Color blind people have been used to detect military camouflage, because they match colors differently.
Aside from monochromatic light, which can be described objectively as a wavelength, color is constructed in the eye and brain.