I've gathered reference images for possible colour schemes.
Ice Caves- The colours truly give the caves a magical quality especially the idea of making the rocks look more like ice than the dull grey which we are used to seeing. The problem with ice is the amount of reflection required for the setting to work and when I include a camera move the reflections would have to move with it which could prove complicated.
Marble caves of Chile- When I came across these images I couldn't believe how beautiful rocks under the ground could be. It seems the Earth hides a lot of natural beauties from us.
And then there's the natural colours of the Earth, white being the usual colour to express heaven and purity. I like the idea of using clear water like the first of these four images, it would reinforce the meaning of purity. I also included images with a recognisable light source to see how light affects the rocks and the colours that are suggesting depth.