Let's say your bush is turning gray, or you just feel like it's time for your mons pubis to get in on the pastel ombre trend. First, dying public hair is quite a process, especially since you don't want to risk ruining your pH balance/life by getting hair dye in places it was never intended to go. You might also risk burning or otherwise irritating your skin, particularly if the color you're using isn't specially formulated for the pubic area.
Then again, if you do want to take the plunge, there's a handy color wheel for determining which pubic hair color is right for you and your busy, muppet-ass looking bush lifestyle. (Blue means your pubes are calm, FYI.)