if I use Aqua Defense or Redguard to waterproof my shower can I just paint a natural color on the floor, or do I have to put tile down. What kind of paint could I use that would not peel up
You cannot use redgard or aqua defense as the final coat. (says this in their product info) Over time standing on them, dropping things or whatever would cause weak points or holes. They are meant to have some type of hard surface on top of them for protection - stone, tile, plastic, and so on.
Paint would not help at all. Any type of paint that got wet would eventually lose binding to the material. Also paint wouldn't help with the above issues.
2 part Epoxy is water proof. Um, what type of shower enclosure? Is it a hand made mortar bed? Normally a shower would have tiles. In this case it would have a rubber basin or like long long ago, some heavy tar paper then the build up.
Red and Aqua, not water proof for continuous direct exposure. Ie, I wouldn't make a bath tub out of either. Tile is best because they (all liners) need protection. If you wear them you will get leaks.