that sounds like the spiny softshell. the FLs an olive green with black spots. the spiny softshells are a tan, mud and caramel would be a good way to describe them. are you thinking of getting it? if you are im sure you know you should research a species before you get it, which it seems you are trying to do. i never used sand as a substrate, i tried but it clogged my filter and burnt out the impeller, and they did fine on gravel in deep water.