What kind of pool is it and does it need a permanant base? If its a blow up pool its a great idea just to lay an old carpet as a protective base for the time the pool is up rather than construct something solid which is a nuisence when the pool is not in use.
Well, even though I am not expert with the swimming pool designing I suggest that you use tiles for the pool base. I saw many pools very beautiful in that. Asking me about the color? You can use your favorite color.