Aquasoil perfector is a substrate to consider as well. Marketed as a soil additive it is simply a clay gravel with a similar size to pea gravel. I used it in my pond the the roots of my plants are everywhere!
Ordinary pool filter sand can look very "natural" depending on what area of the country you are in. That sand isn't controlled for color, just other properties. Mine is a very natural, but light color.