Your Halloween jar could be left as is or you can colour the inside of the jar. There are various ways to do this: one way is to colour it with Mod Podge or Decoupage paste mixed with food dye (a few drops each of yellow and red); or as I did, add a little water to orange paint to make an ink-like consistency. Pour the paint into the jar and swirl around until all the inside surface is covered. Hold the jar upside down over a receptacle to catch the drips and left over paint. I left my jar sitting upside down, resting on a couple of plastic pegs inside a plastic disposable plate for an hour or so