How The Sky Could Actually Be Not Blue

People will often ask the question "What color is the sky?", or "Is the sky blue?", usually with verbal irony to point out that something is obvious or indisputable. But really, now. This conclusion that the sky is blue is really based off two assumptions, and where there are assumptions, there can be mistakes. So let us, truly, examine the question: "Is the sky blue?", beginning with two assumptions.

First: color is an inherent property in things, and is not just perceived by an observer of these objects. But honestly, who is to say that color is something that is inherent in the universe. How could you convince someone that color is real, and not simply something your brain adds to the world to try to make sense of the reality in which it exists? Or is color really a property of something, because two people can look at two things of the same color and match them together consistently? Well, the truth (as usual) probably lies somewhere in the middle. The difference between whether something is inherent or perceived depends on whether or not the property is quantifiable. For example, thermal energy is something inherent in an object, but whether is is hot or cold is subjective, and therefore, perceived. Applying this to color, color itself can be said to be inherent. You can measure the wavelength of light, and since this is what gives light "color", then it is quantifiable. But the instant we say something is "green", or "dark" or even "bright red", we switch to color being perceived. This is because there is no way to measure "greenness" or how bright a color appears. In summary: color (or rather, wavelengths of light) is technically an inherent quality; but it's experienced subjectively, and is therefore (to people) actually a perceived quality.

Second: people have no way of knowing that the color they perceive as "blue" is the same blue for other people. This is the real crux of the matter. Since color is actually perceived, and subjective, there is no way to know that your mother didn't see the sky in a color you would call "green" or "brown", while you see it in a color she would call "orange". Your mother taught you the color of the sky is "blue". However, there is no way to teach you what the actual color blue really looks like, because it is impossible to try to prove that you two are experiencing the color in exactly the same way.

So between color being a subjective property and the uncertainty of how it is perceived, the sky could (in theory) be not blue to you compared to anyone else's "blue". One could argue that because we both give the name to that perceived color "blue", it is as good as the same, because we both think  of it as blue. But the name and the color are two completely separate entities. So yes, the sky is "blue" (according to you), but in reality, it may not actually be blue (according to everyone else). It could be red. They key word here is could. So the next time you think "The sky is blue.", now you know to doubt even that axiom of your existence.