When I did my first BH mystery, Roll, Roll Cotton Boll, it required a bunch of neutral strips. I remember opening the bin with my shirtings, taking a look, and then thinking that I needed to "save" them. Then I slapped my forehead and said "what for!" Then I happily cut many of them up into 1.5, 2, 2.5, and 3.5" strips and my scrap saver system was born. That quilt also required pinks, greens, and browns. I did the same thing with those colors, even cutting into some yardage. When I did Blue Ridge Beauty, I added a bunch of blues. I think the key to getting started is to cut up the colors as you need them. Often times now when I'm fabric shopping, I'll buy quarter or third yard pieces to add to the bins. It is so nice to be able to do scrappy quilts by just grabbing a handful of strips that are ready to go.