You can use granite counter top sealer to change the color of the granite, but there are sealers that will not change the color of your granite if you do not want it changed. Be sure to look for sealer with regular impregnators. This will immediately absorb into the granite, not having an effect on the color.
The other kind of sealer is called color enhancing sealer, which allows you to choose a color to brighten, or even change the color of your tile. This sealer is very effective if your granite starts looking dull or if you want to completely change the look.