One of the benefits of a "mix" substrate [= one containing more than one colour or shade] is that "stuff" is not so easily seen. I've used natural gravel (the beige/black/white/brown mix) and a similar in black/gray/white which is darker, Flourite black (solid black) and play sand which is a mix of black/gray/tan/white. In the past I've also used the natural pea gravel size and the Birdseye gravel.
I have been resetting my tanks over the past year, and moving to playsand in each of them. Interestingly, I find the black to be "lighter" under the tank light, and a real disappointment [in more ways than just appearance
]. I am very fond of the play sand. It does darken after a few months, the fish do seem to like it, and I know it is authentic because it replicates the sand in many Amazonian streams--which may well be why my corys are so happy and spawning now.