You said it was a Gameboy Color game, this Narrows down details. Look on the back, if the screw is Phillips, your game is a bootleg. This means that it was produced illegally by someone trying to make profit, and instead of being a real manufactured game, someone just put a ROM dump on it. Also look at the top of the back, if it says nothing on the little bar, it is also a bootleg. Look on the front, if the label looks a bit sketchy, or the top reads "GAME" it's a bootleg.
The reason you don't want a bootleg game is because if you have one, the battery is going to be really unreliable and won't work right.