3M Colorquartz. You can basically choose between any color or combination of colors and between 2 sizes.
I myself got the black S-grade; 50 lbs. bag x 5 for $17.70 each. Got if from a pool builder supply company. Most who sell them do not sell directly to the public, but they will if you are just getting a couple of bags.
Even this black is pretty clean. 10 minutes of running water and it is clean. It is heavier than sand so it sinks quickly with no floating particles.
The S-grade is uniformly shaped and compacts nicely. The T-grade is bigger than sand, but much smaller than gravel with irregular shapes.