2 pieces black granite that are the same, 1 w/ gold hilites, 1 w/o. Will the 1 w/o change color 2 have gold?

the saleswoman told me that one was exposed to more sunlight, and that is why the gold highlites are in it. she also said that the one that is all black right now will eventually get the gold highlites. is there any truth to this. at first i thought she knew what she was talking about, but the more questions that i asked, the less i believed what she was saying. i dont know what to do. buy the one with the gold because i know what it looks like, or buy the one that hasnt "changed" colors yet, and expect it to change over time. and if it does change, how long does it take? thanks for any help that anyone can offer.