I would expect rain to be formed from a dark grey cloud.
A cirrus cloud.
Nimbostratus Cloud
The dark gray cloud that blankets the sky and often generates precipitation is called a nimbostratus cloud. These are also clouds that extend far both vertically and horizontally.
Dark gray and flat or really dark almost black and puffy
the name of the cloud full of rain isz cumulus....misz.remynisce
cumulonimbus
Nimbus clouds are dark gray cloud bearing rain. So, yes.
The funnel cloud of a tornado is full of water droplets just like an ordinary cloud. As a result it blocks light and may appear dark. A tornado may also appear dark if it is lifting large amounts of dark soil into the air. However, not all tornadoes are dark in color. Front-lit tornadoes may appear light gray or even white. Depending on the soil some tornadoes may be light tan, to reddish brown, to gray in color.
They are often dark gray or even black, but not always. In terms of color they could look like fairly ordinary storm clouds.
GRAY
Blue grey, dark grey, warm grey, cool grey, cloud grey, silver.
Cumulonimbus cloud's colour depends on the conditions, time and your location. In broad daylight, with the sun shining on them they are usually white, like all clouds in daylight. The base of the cloud is dark grey because of the thick cloud blocking the sun. Depending on the cloud thickness, the underside of a cumulonimbus can even be black. When there is a lot of hail and ice crystals in the cloud, it can take on a green or turquoise appearance. In the sunset, the cloud can appear brown, orange or red. At dusk, the cloud can appear light blue, and at night, it is usually hard to see untill lightning illuminates it.