why are rain clouds and snow clouds black?

Storm clouds and snow clouds are darker in color because of two reasons. First is the most known reason. These clouds are holding a lot of water molecules and ice crystals. This makes it harder for sun light to penetrate through.

The other lesser known reason is that these clouds often grow high up into the atmosphere, sometimes reaching close to 50,000 feet up in the air. The shear size of the clouds also makes it harder for sun light to penetrate through.

Actually they're usually greyish white but if ur talking about the big storms:

The size of storm clouds are very high causing sunlight to be blocked out

The huge amount of water in them also blocks out the sun

There may be a lot of dirt inside the cloud

The clouds that produce heavy rain or snow are typically cumulonimbus clouds. Cumulonimbus clouds are characteristically high. Since they are higher they have more of a shadow.

They have more moisture built up in them and are thicker, so they produce more of a shadow. :)

they are thicker with more moisture (snow ) water)(