Sandblasted Granite

We had Sandblasted Absolute Black Granite installed in our kitchen 3 months ago.  We originally applied 4-5 coats of sealer before using.  Over time I've noticed blotches and streaks appearing in areas of heavy use.  These are darker in color than the rest of the countertop.  Not sure if they are from food oils or from abrasions.  Any ideas?  I've been told that Absolute Black can naturally produce such spots, and that they go away on their own.  Also been told that oily stains will eventually dissipate on their own.  Suggestions, please.