But truly, a Realist would say that the existence of "redness" is not dependent on any factor "in" space/time, it is "beyond" space/time. Thus, time passing - bringing observers into and out of existence would have no bearing on the existence of "redness". Neither indeed would the collapse of the universe altogether, which would obviously eliminate all corporeals, wave lengths, etc.
A Nominalist on the other hand, would require a physical universe and "redness" would have no existence whatsoever.
I don't really see how the two views can be reconciled - though it would be nice if they could be...
Have you tried 'Sharpism'?