I use black sand in my 55 gallon (national geographic brand) and i think its very unique. it makes my plants look greener and it makes the colors on my fish stand out more. Plus i have heard darker colored substrates make fish/invertebrates feel more comfortable.
I think it sets my tank a part from a lot of others' that I have seen but it isn't "unnatural" as if you would use like a red or blue sand.