No, I'm not too worried about cross breeding or producing odd colours. I'll just let nature take its course. The substrate is Fluval Stratum, the red coloured bag one. I was pretty scared at first when I used it, my tank water was black!! But it eventually cleared up.Yeah, you should check a cross breeding chart for compatibility, if you're worried about keeping the same colors and not dulled out browns eventually, but otherwise I love it. The cories are cute, and the black gravel really makes the shrimp pop.