I was going to suggest the Home Depot or Lowes, or your local hardware store. They all carry colored electrical tape. It takes more work to use electrical tape because you will likely put the white down the first the full width. Then you will need to cut the red and green about 3/8" wide. Then apply them carefully so they are evenly spaced.

One advantage of electrical tape is that the color is in the tape rather than an ink on top of the white tape.