Melt multiple colored strips together with a heat gun, then take a long tonged fork and drag it across in one direction or multiple directions to form patterns before cutting the plastic into shapes. Having your metal cookie cutters in cold water before use makes the cutting easier.
STEP ONE: Melt multiple colored plastic strips together.
STEP TWO: While the plastic is hot, comb it in one or both directions.
STEP THREE: Cut into the hot combed strips with cookie cutters.