The sky is obviously blue, but there are a lot of shades of blue in it. And clouds. And it changes at night and during sunset. Etc.

Okay, but in plain language, it wouldn't really make sense to say something is obvious and then to say there are many exceptions, no?

Obvious doesn't exist. Everything is learned.

Obvious just means "given our context, we don't expect to require much complex thinking to get to that conclusion".

It's just another convention.

Given our context of most of us having eyes and color receptors calibrated in a similar fashion, I expect most people will see the sky blue. Of course if you dig deeper, it opens the discussions to nuances.

It's the same here.

Nothing wrong with that.

It's obvious yet complex that the obvious can also be complex