Apparently it's all true!
Since leaving the cult and happy valley for AZ, forsaking our temple covenants and magic underwear, and abandoning the mormon dress code, DW and I have found our skin darkening most dramatically! The effect has been even more pronounced with Sundays spent out and about in the Phoenix area instead of in a chapel. And the longer we're out, the darker we get!
Of course we are sure this has nothing whatsoever to do with Mediterranean heritage, or with the beautifully sunny weather down here.