Polymer clay presents so many ways to use just the clay itself (without paint etc) to create complex color blends and designs.   

The Mokume-gane technique involves (usually very thin) layers of clay stacked, and impressed with deep stamps, texture sheets or household objects such as knitting needles, pen tops, and various hardware.  (The name is based on an ancient metal technique which involves patterns created by cutting into thin layered metal sheets)

Once impressions are made, very think slivers can be removed with a flexible blade, so you can use the sheet of pattern that remains as well as the slivers you’ve removed.