I've tried every setting to get the clouds to block out the sunlight, but to no avail. I've had cumulus clouds a kilometer thick which in the real would would definitely keep the sunlight from getting through and would also look quite stormy, but they still glow as bright as a thin cloud would. Andchanging the cloud's color to black only seems to make it completely vanish from the scene, almost as if the clouds a 'screen' layer in photoshop.