How do you read the following map?

משה 0

What does the color of the cloud mean?
And what does the 212 k symbolize?

idefix37

This is the brightness temperature of the top of the cloud. It is measured by the infra red sensor of satellites.
The higher the top cloud is, the lower its temperature is. When it turns to red, it is not hotter but colder. This non conventional way to show temperature is used because these high cloud tops are the signature of cumulonimbus which can give very strong thunderstorms (red = danger)
In your screenshot, the temperature is expressed in Kelvin, but you can change it in °C in Settings.