Stencilling is a colouring added to the surface of the concrete and it will discolour and leech out if it is not sealed correctly. Sealing is an excellent idea for stencilled concrete. Adding a sealer will make it easier to clean and it will not require cleaning as often.
Bunnings has a few products which can be used for sealing stencilled concrete. If you were after something off-the-shelf, then White Knight Ultra Pave Clear Sealer - 4L is suitable for stamped or stencilled concrete.
An excellent premium alternative designed specifically to go over stencilled concrete is the Crommelin surface treatments. These products are available through our Special Orders desk at your local store and are of very high quality. Here's a handy specifications document on the preparation and application of Crommelin sealers.
Before sealing, I would advise giving the area a thorough cleaning with a pressure washer and allowing it to dry completely. You don't want any discolouration, contaminants or moisture left in the concrete. Any contaminants will be permanently trapped beneath the sealer making them very difficult to remove later and can compromise the finished result. - MitchellMc
Please make sure that your driveway is totally dry before you begin to seal it. Also be sure to wear personal protection such as gloves, goggles and a mask when applying the concrete sealer. Make sure to follow all the safety precautions indicated at the back of the container. - EricL