CBSE Class 10 Answered

Thundering generally occures when its about to rain.Clouds are made up of tiny water droplets or ice crystals, usually a mixture of both. The water and ice scatter all light, making clouds appear white. The gray colour comes when there is more water vapour in the cloud. This will blocks the ability of light to transfer through the cloud. If it is transferred this will be white. Light is energy and water absorbs the heat that is within the light. Higher the density of the cloud higher the absorption of energy in the light. This creates the dark colour. Higher the thickness of the cloud, harder for the cloud to let light pass in, therefore creating the darkness inside and out.
Also, if there are lots of other clouds around, their shadow can add to the gray or multicolored gray appearance.