Constellations would be an interesting theme. Serpens, the snake constellations, are particularly awesome. Apparently it's the only constellation that is distinctly 2 parts (head and tail), separated by Ophiuchus (the handler), complete with the star Unukalhai (serpens' heart).
In the process of trying to find images of the serpens constellation, I came across this flower, which I really wish existed in the silk variety: Agapetes Serpens . (If anyone finds such, please do let me know). Small red trumpet shaped flowers would work really well along the top/back of a viv or underside of decorative bridges. Alas.
http://www.google.com/imgres?imgurl=...QEwAg&dur=2496