Every time I've played with real clouds they come out as crap.
The synth clouds are great due to the degree of control you have over them.
But having clouds as a seperate layer, lets you do blurring and touch up effects on rough areas with the clouds. (like when you have a high Coriolis force)
Proper color is the key as Thunder said, you need to keep to a motiff for a planet.
A purple planet with green oceans can come out looking realistic with proper selection of colors, clouds, and atmosphere tones to blend it all together.
My only problem with Lunarcell is that the more I play with it, the more my planets loose their "hard edge" and begin to look like matte paintings...
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AceStaff member FreeSpace Watch
http://freespace.volitionwatch.com/