I've had the sand for a long time (6+ months), so it's not a matter of cloudiness or type. I don't remember what kind it was, but think it's aquarium sand. The issue is it tends to look gross pretty quickly with poo and discoloration (weekly cleanings), and no matter what I have to do additional filter rinses post water-change to avoid back-up. The gravel was just so much easier to maintain and it looked better. Also the loaches don't really burrow/dig that I've seen unless they're going for pellets, unless that's all surface level? Even then, they seem to prefer to swim around, hang out on filters, drape themselves on deco, etc.
I'll look into natural colored gravel, but if you have any additional detail that would be great. And if they just won't be happy with any gravel I guess I'll just continue to deal with it, was just hoping a gravel could work...