Every day we must see the sky but many who do not know beyond the height there is a very beautiful scenery. Both in the daytime and in the evening, while the clouds still look beautiful.
When it rains clouds will look dark, not white like when sunny. When light has all the colors, our eyes look white.
But as the thickness of the clouds is still thin, the clouds pass a large amount of light that redeems it and looks white. As the cloud grows thicker, the more reflected sunlight and the less light it can penetrate the clouds and the undersides of the clouds appear gray instead of white. Due to its thickness or altitude.
This means the clouds get thicker and denser as they collect more water and ice crystals. Make the particles at the bottom of the rain cloud. White is why the overcast cloud looks grayish and dark.