Hi Matt,
I had the same issue when constructing my "dream" layout. Had never done any of this before, so followed advice from various sources. I suggest using blue hues, going lighter as you descend towards the layout. You can also create clouds fairly easily. I did this by creating stencils, then spraying white paint a few inches from the stencil onto the wall. I did several practice attempts in the garage before moving to the wall. See photos.
Hope this helps.
Michael
