I suspect some Greens will take a spectral analysis of cerulean, point out that it differs from standard blue paint and that there’s some green in it, and argue that the sky really is green after all. A new debate might start on the proper definitions of “blue” and “green.”
BTW, what happens if the sky is overcast and gray?
It might be worthwhile to list statements about present-day society that would have seemed incredible to me at various times in the past. For example:
That nobody has been to the moon since 1972.
That the Soviet Union no longer exists and there has been no nuclear war. (One or the other would have been plausible but not both.)
That we’re still using fossil fuels on a large scale.
President Ronald Reagan.
That there is a major communications network that is not run by any single organization.
That there would be a high-quality computer operating system based on free software.