• Set FOV high (also works without, but the effect is clearer)
• /time set night
• Turn towards the sun
• Look at the right side of the screen: Sky is pretty red.
• Turn towards the moon
• Look at the left side of the screen: The same part of the sky is now more blue.

To be clear: The exact same part of the sky changes its colour, it's not just a different part of the sky. If needed, star constellations can be compared.

Another way to reproduce:

• /time set night
• Turn towards the sun
• Go into front-facing third person mode (the one where you see behind you)

Result: Moon with red sky around it. In the other direction the red part of the sky around the sun is much smaller than usual.