oooh, and if you’re going to showcase the clouds, you may want to use the rule of thirds...
two thirds sky on top, one third landscape below. One third castle to the left, two thirds clouds to the right. Buster's little butt sitting at the intersection of the bottom and left third, so the balance of him is visible against the sky.  This should work as far as colors too.. him being flame point (orange based) and sky being blue based) you're going to get a very striking complimentary color combination for your focal point. 
I would make the ground some sort of a coloring analogous to blue, but little toned down, perhaps green/blue, cool haze coloring. For the castle, go with something analogous to buster, perhaps some sort of a non-descript warm taupe as the main color. Something analogous to orange/beige, but not overwhelming it.

I dunno if this will work, but it's an idea you may want to try ;) 

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