Cloud trivia: why there are often dark clouds when it rains in summer

When summer rain comes, there will always be a lot of black clouds. Why is this?

These are cumulonimbus clouds.

In summer, there is plenty of rain, and there is more convective weather. Cumulonimbus clouds absorb too much rainwater, up to the top of the troposphere, and can even block the sky. When it rains, it is very heavy. In winter, precipitation is a rain cloud Cumulus clouds cannot absorb too much rainwater, so it cannot compare with summer when it rains.