Here's a nice TRICK that I found REALLY helps a lot. 2-D Cloud Planes are often a bit THIN and light easily passes through them. In some cases this is great for special lighting effects. However, many times you want a more SOLID looking Cloud and the way to get this is to make a COPY of the Plane- and then go over to the POSITION Doo-Dad Widget Thing and touch the spinner dial just ONCE! This nudges the SECOND plane a very tiny distance APART from the first Plane- and your clouds will look more DENSE and THICK. DON'T do this "manually"- as it causes a MIS-REGISTRATION of the two planes. The "Y" Position Click keeps your second Plane in Perfect Alignment with the Camera!