heyas; i find it's difficult to tell what part is doing what effect in the preset skies, so when i mess with them, i try to start with a blank slate to learn what's going on. first, when i start a new scene, i pick the 'no atmosphere' setting. no haze, no clouds, blue sky, yellow sun, very basic. then click the sun icon to mess with the lighting colour, the ambience, etc. click on the fog/haze thingy to create atomspheric perspective. click on the cloud icon to make cloud layers. when you create layers, you can control their altitude, and load a shader for them. load one up from the cloud material directories. note that the same shader may look vastly different depending on if you put it at a low altitude or a high one. so play with that for a while, and move the sun around and all that good stuff. :)