Pour a small amount of one colored syrup into 1/2-cup molds for a first layer, making it as thick as you like. Freeze until firm, 30 to 60 minutes (a thin layer will freeze more quickly). Pour a second layer into each mold, as thin or as thick as you like. When layer begins to set, after about 15 minutes, insert a wooden pop stick into each mold. Continue to freeze until firm; straighten stick as needed. Continue making layers until each mold is full. Freeze until hard; overnight is best. Pops will keep for at least 3 weeks in the freezer.