More likely that centuries of aging, oxidation, and exposure to soot from non-electric light sources have dulled the original colors to what we see today.
Art restoration experts face a constant battle in finding a balance between the original appearance of the painting and what people have come to expect the work to look like.
Rennaissance paintings often had brilliant colors that were lost over the years and would shock those used to the muted colors we now see. Even 19th century paintings often look nothing like they did originally because of the varnishes used to protect the paintings.