Place your colored piece on a square of parchment paper, on a tray in your toaster oven (preheated to about 250 degrees). Watch the magic happen! Don't worry... it will curl up. and curl up again. then finally settle down to the smallest size.
If your oven is already hot, this will happen almost immediately and take maybe 30 seconds to complete the process. Keep watching!
Sometimes, if you have a long skinny piece, it may turn on it's side and curl up. That's fine, just flatten it out when it's done.