Well, if you plan on using your pet as a showpiece...then I can somewhat understand the concerns over "color fading". But for the enrichment of the animal, and overall well being, a decorated cage with lots of things for dragons to interact with is always a good thing. Perhaps adding more light intensity will combat the issue?
As for rock sculpture ideas, the best one to start out with is usually a basking platform. Easy enough to learn the whole process, yet completely functional for the animal. The first basking structure I ever made is still in use. I eventually graduated to much more complex pieces, but you gotta start somewhere. Start with a platform, then make a hide, then make a background rock wall. Any of the above would look great in a cage.
As for supplies, there are lots of threads on the subject. But basically you'll need grout, foam, and a sealer. I'd go into more detail, but like I said....already been covered in numerous other posts. There is one just a few threads down in this section, I posted a list of appropriate sealers + some hints and tips about the process.
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