Some go according to pattern like all dots, gingham checks, florals, colors, such as black and grey, black and white black any other color. Nothing but neutrals which could be, black, shades of grey, beige, brown, creams etc. Sometimes one pattern material and pull similar colors from it. It all depends on what it's for. Many piece odds and ends and use for a backing on a donated quilt. Some have left over knits, linens, cottons, just all depends on the moment an what the situation calls for. I try to keep like colors together. Blacks, browns and beiges, greens, reds, pinks,yellows, I have found if I keep according to the color wheel, I'm good. Also each color usually has 2 bins 1 1/2 to 5" scraps. Then up to 1/2 yd. Anything larger than 1/2 yd goes on a fabric board. I usually pin a note as to what is left after use. If there is 1/2 yd or less it goes into the scrap bin according to size.