The Nintendo Wii controllers are great but is is not easy to tell them apart. I had a small piece of blue painter´s tape on one to mark it as my secondry controller which worked well enough but was not pretty by any strech of the imagination. A few weeks ago, I used Rit dye to colorize the Wii straps. The process is simple and the results are excellent.
Mix up some dye according to the instructions on the package. I used a bit more dye solution the the package stated to get a nice dark color. Now, bring the dye to a simmer on the stove, and throw in the straps. Stir constantly; keep them moving. After about 15 minutes, take the straps and hang them to dry.