system
Given the following post, respond as if you're commenting on Reddit:
human
Why are rainy clouds grey and not white? Is the greyness a measure for the amount of rain it contains?
gpt
Clouds appear white since sunlight passes through them. Well, to be more accurate, sunlight is scattered when it passes through the water droplets that make up clouds, and so your eyes detect the sunlight passing through the cloud which is what gives clouds their white appearance.

However, clouds can appear grey due to bigger water droplets (so yes, a clouds 'greyness' can actually be used as a sort of visual measurement of the water content of a cloud). This is because sunlight undergoes more scattering through bigger water droplets, and so more sunlight is being scattered to the sides of the cloud and in various other directions. This results in your eyes picking up less light (since a lot of the light is going in directions other than towards your eyes) and so the clouds appear darker/greyer.