I have done a few mystery quilts for my quilt group. The very first one I did was one I found online. I emailed the designer and got permission to use it for my group. It listed fabric types to be used. When it was all finished, the comments I received were mostly to the tune of: It's ok, but if I knew what it was going to look like, I would have chosen different fabrics. Bummer for me and all my work putting it together. Several years later, I was asked to do another. This time I did a scrappy mystery quilt, again found on line. I joined up and saved all the clues. Then the designer put it on Craftsy and I bought the pattern. I broke that down into segments that worked for my group. We did it as a clue every week instead of once a month. The last mystery I did, that I think was the most successful, was a scrap quilt mystery that I basically designed. I picked out 2 blocks that worked very well together and broke them down into cutting, piecing segments, etc. etc. etc. and again did a clue every week. My suggestion to you would be to do a scrappy quilt with the same fabric used for background. I personally don't like things that get to be too busy, so having the same background fabric makes the design jump and you get to use up a lot of scraps. My Carolina Home does some awesome "Scrap Dance" mystery quilts. That's where my first scrappy one came from. I've been asked to do another, but since we're in the process of moving, I think it will wait for next year. Good luck.