The only way you will get 'mud soup' is if you don't understand color "value" and how to use it. By "value" I mean how light or dark a fabric is. Normally, you have your lights (neutrals), darks, and your mediums. Then, to make it more interesting, the same fabric value may look like a dark against one fabric, and a medium or light against another, and it's totally fine to play them that way in your quilt. To keep a scrappy quilt interesting you need to know how to choose which fabrics to put next to each other. You need contrast. Otherwise... mud soup.
I'm sure it's easy to pull random scraps out of a bag and sew them together, but that won't get you the prettiest quilts. You need to discern what goes against what, and not leave it up to chance.