Why do storm clouds look black?

Particulate, refraction, light absorbtion? Eeeevil? (puts pinkie finger to corner of mouth)

The thickness of the moisture content prevents light from penetrating? Just a guess. Can’t figure what else would make them dark, especially at midday.

Yep, it’s the thickness. A cumulonimbus cloud can be tens of thousands of feet high–virtually no light can get through them.