Here is a suggestion for the Air-Entropy Card backing ... It was done fairly quickly on Bryce7, but it seems to fit ok.
I find the idea of a purple sky as representation of entrophy quite good - I mean, clouds are chaotic and form quite unpredictable structures in the sky in which we may, with a bit of fantasy, recognize cloud images.. what could ever be more random than that?
That totally rocks!
shadow303's entropy life mix is the most colourful mark in my opinion.