i hear you... you are wrong, of course, but i hear what you're trying to say. why a blue sky? since we're on this, this is EASILY provable with just a TINY bit of research of wavelengths and the layers of the atmosphere. it's not rocket science, lol, it's actually particle science and chemistry .
Well, at the primary level, the issue is one of definition. The sky appears to most humans in a color most humans perceive as blue (under certain circumstances). THis was an observation in a sense, that became part of a defined view of the sky. THe reason I like the analogy so much is simple; the MOwgli/MrSomebody types remain at this level of discourse, i.e., the pre-scientific revolution level of "observe, assert, pick your ass if somebody disagrees."
At the higher levels of observation and research, humans have learned that light refracts in Earth's atmosphere in a spectrum that appears largely blue. This second level of proof, causality, and scientific rigor escapes the Mowgli types.
Then there is another tier, one that requires strict mathematical proofs, and requires testable, disprovable theories. The Mowgli types are completely lost long before they reach this level, so they latch on the terms "Theory" and "Proof" and apply the common definitions of said concepts, not understanding the extreme rigor required for a "Law" under science.
It's so pedantic, my friends.