Lightening / Bleaching Travertine Floor Tile???

I recently received an order of "light" colored travertine floor tile. Only this is, it's mostly "medium" to "dark" in color. The vendor told me that because it's natural stone, it's subject to "natural variation" in color. I accept this answer, but I'm not too happy about it.
So what I'd like to know is this: Is there any solution that I can apply to the tile (hydrogen peroxide, bleach, etc.) that will lighten its color? Is there a commercial product available? Is there anything the tile installer can do, perhaps with a certain type of sealer?
Thanks very much.
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