Why is the color saturation higher on cloudy days than on sunny days?

This is also a phenomenon of chromatics.

When the saturation is high, the color brightness is usually small.

The saturation is low when the color brightness is high.

There is no strong direct light on cloudy days, so there is no strong reflection on the surface of the object, so the color brightness is low, but the diffusion on the surface of the object is soft, so the saturation is high, but you must find that the contrast between light and shade on cloudy days is very small, and the sense of body is not as good as that on sunny days.