just make it blue. There is no way you can do clouds. Maybe do some sort of light gradient coming from the bottom or top. (i.e. a lighter blue background with a darker blue gradient..or even a gradient to show a setting sun..which would be something in the warm colors category).
I say stick with the blue, jibtastics idea of a lighter color is cool, but personally I really like the contrats between the orange jumpsuit and the darker blue sky, if it was a warmer color the contrast wounldn't be near as dramatic. But thats just me.
But, make it blue, with a slight gradient, and your set.
