It gets down to personal choice on what looks right but I find I like a mixed variety of things as that is what I find in nature when I look at the bottom of most places in freshwater. I rarely see a single bottom but most often it will be different sizes, types and colors as the current shifts and changes.
So how to get a mix of colors and types? Wait long enough and you can start out with a single item like the whitest white pool filter sand and then you may find you put a pot of dirt in one corner and another here and there and after a time they get a bit spilled here and there, so that you get the mixed look which I call natural. It doesn't really take work, just time and ignoring the question!
When I start with a sand and find it too bright, I now just cut in a bit of some darker color to let it tone things down. No harm in having the "too bright" pool sand mixed with something common like "aquarium gravel, play sand or dirt and if they are in the same tank and you do any amount of switching and changing, they WILL all be mixed.
So don't sweat it, just use what feels right and then add more to adapt it as you feel right.