Some of my fabric is sorted by quality or anticipated projects in plastic bags or baskets. My stash covers so many years that I try to not mix the older stuff with newer fabric. Also, if I paid a lot and I like it a lot...it stays separate no matter what color it is, my system is atrocious and could not recommend it. I do keep whites, creams etc together tho. That is important to me. But mainly, I try to keep complementary fabrics together or I might wind up using that perfect matching color on a new project. Also, very important...I keep my wip quilt tops and the extra fabric together until the binding is sewn on.