The source image for this Liquib sample image was a picture of the sky.  Numerous Clouds were then applied with the Cloud Coloration set to Scattered Showers.  Cloud Coloration is specified by Front and Back Tints, and several standard pre-set Cloud Colorations are available, or the Tints can be selected manually (or randomly).  In this example, the Backlit Clouds option has been set for many of the Clouds, causing the Front and Back Tints to be reversed, which essentially makes the sunlight appear to come from the opposite direction.  Cumulus and Stratus Clouds are shown, created with various size, Density and Puffiness values.  The resulting Clouds are fairly realistic (although this particular grouping and mixture of types would certainly never occur naturally).