To quote Harriet Hargrave, "Scrape quilts depend more on the effect created by the use of light, medium, and dark, as well as texture from the print, than they do on color. If you look at many old quilts, you'll find that more times than not the colors do not relate to one another, but the pattern emerges because of the value changes and surface (print) interest in the fabric.
"Begin by sorting your fabrics, scraps and all, into three piles: light, medium and dark... As you sort through your fabrics, you may find that these piles are becoming stunning color combinations for a quilt. You almost can't have too many fabrics when making a scrap quilt -- often the hardest part is deciding which ones to eliminate.
"We often buy fabric because it's 'pretty,' ignoring the value and texture completely. If you were to examine old scrap quilts, you would find fabrics in them that you would not consider buying. There are even complete blocks that we don't care for when examined individualy. However, when you look at the overall quilt, the effect is wonderful. If you're serious about making stunning scrap quilts, you need to make an effort to break out of buying only the pretty fabrics and start collecting some 'dogs' and 'uglies' so that your quilts will have life and depth."