A Most Peculiar Sunset

You wouldn't know it, not right away, but there is something strange about this picture. It's a sunset, yes, but notice the blush of color right above the sun. It's blue. And as you look up, the blue fades into a faint rose or pink. Now think about the sunsets you've seen, how often the sky can turn golden, or orange, sometimes pink, red, but when you look up, away from the setting sun, those colors fade back to a pale, twilight blue? It's rare to see a sunset dipped in blue. So this photo is a puzzle: it's blue where the red should be and red where the blue should be. Why?