Why is the sky sometimes yellow?

Personally, I think this is the reason.

First of all, we don't rule out the cause of the sun. Because sunlight is composed of seven colors, you may be in a specific environment (about air humidity and other conditions) at a specific moment, because the sky is yellow in a specific mood.

Secondly, I think it may be because the sun sets around 3~5 o'clock, or at dawn in the morning, you can't tell if you can't see a specific scene in a specific geographical location ~

Third, it may be because of the mood ~ sometimes you think this thing is blue, it is blue. If you think it's gray instead of blue, then even the blue sky will have a gray layer to you.

It's purely personal, please don't mind.