I figured that dark colors would work best, so if you get yellow, you may be sad with the results. Take your box of dye home, and mix it with 1 cup of boiling water on your stove top. Keep the mixture on the stove, and then stir in your strap(s) (I found that 1-2 straps per bath works the best). Stir it around and make sure you move the plastic on the strap around or you'll get a light spot. When you're happy with the shade, rinse the strap under hot water until it runs clear, then under cold water for a few seconds. Let it dry and you're done!
Step 2: Put the dry strap on your Wiimote.
That's it! Your colored strap can go onto your Wiimote and you're all done!