I have a problem with water faucets.
When I see the blue and red color-coding, I freak out. Right now, I’m setting comfortably at my desk, so there is no problem. The blue means cold water and the red means hot water. As everyone knows.
But when I was a physics undergraduate, I was taking upper division mechanics from Professor Joe Tenn. One day in class, he mentioned that he had been at a health club taking a shower and he noticed the blue and red color-coding. It was strange, he said, because blue light has more energy (per photon) than red light. And so it made sense that blue would indicate hot water and red cold water.
He knew, of course, that red indicated hot water because fire was red. And blue indicated cold water, because—the logic kind of falls apart here—blue stands for water and it is cooling and thus cool. But this didn’t make the faucet color-coding any less frustrating—for him, at least.
The truth is, that when Professor Tenn said this in class, I wasn’t that clear about photon energies and such. Not like now when I have the Planck constant memorized to 6 significant digits, despite myself. Graduate school was when the problem first occurred. That’s when light really became important to me—largely because my entire PhD dissertation was about atmospheric light scattering. That was when I started to think like Professor Tenn had taught me.
At first, there was no problem. But after a while, the “blue has more energy” logic became self evident. Just like the “fire is hot” logic was before. And then my usual meta-logic of “faucets use the logic that is obvious” started to fail me.
Now, I freak out when I look at a faucet. But if I manage to remain calm, I can work it out. But now, my meta-logic is, “Faucets use the logic that isn’t logical.”
 Stay tuned for my explanation of why the sky is blue. It is not the standard explanation about blue light scattering more than red. This is true, but that’s doesn’t go very far to explaining the things we see. For that, you need just a little atmospheric chemistry. I promise it won’t hurt. Much.