Why are some clouds bright white, and others dark gray?
Next time we have some puffy cumulus clouds, take a careful look at them. You'll probably see the part of the cloud facing the sun is bright white-perhaps dazzling white. That's because the cloud drops or ice crystals reflect sunlight very well. But the side opposite from the sun, and probably the base, is fairly dark. That's because much of the light is reflected, leaving less to pass through the cloud and illuminate the base. And because that part of the cloud is 'in the shade', it's also darker.