The original search was for why the circuit board pads had turned dark. I had turned up tin-pest, however, LMI pointed out gray pads after things lifting off which pointed me to intermetallics (link in post #8) as another possibility for the gray pads. Intermetallics form as copper get into the tin. Both intermetallics and tin-pest are crystal changes in the structure of tin (phase).
I am not ruling out tin-pest, or an intermetallic, but at this time think tarnish from sulfur seems more likely, and it happened much quicker than I had expected on the new boards. The chia pet reference is from the link in post #2. It refers to creep corrosion and involves sulfur and silver (as tarnish) that cause a galvanic reaction with copper. Sulfur is used for vulcanization* of polymers, so is found in plastics and rubber, both of which outgas** with heat and age. Creep corrosion can be clearly seen in the image of my OP, but I had no clue what it was at the time.
*Vulcanization - Wikipedia
**Outgassing - Wikipedia
As far as lead-free solder being fixed, I am convinced that is wishful thinking. Even if the board pads are ENIG which can stop continued intermetallic formation, is a tin-rich solder really immune to tin pest. Here is some info on how to test for tin-pest in tin-rich soler*. Also do the parts soldered on the board limit intermetallic formation.
*http://electroiq.com/blog/2006/11/tin-pest-in-tin-rich-solders/
Another problem that keeps showing up when I search is Tin Whiskers*, which again is related to tin-rich surfaces. Some are saying these are extrusions caused by tin-pest.
*http://www.maximintegrated.com/en/app-notes/index.mvp/id/5250