A Rather Odd Question

Don't know for sure what chemicals cause it, but typically it is because the ring is cheap and of not good quality.

Without pretending to be a complete authority, I think what you are seeing is nickle oxides rubbing off the ring. It certainly has nothing to do with your iron level.

Physical changes in hormones and just about anything than can affect the skin through skin oils and perspiration play a part. So can chlorine and cosmetics. Salt from the body in the form of uric acid is another possible cause.

Even white gold has nickel in it. You should be able to tell the quality of the ring by the stamp indicating the gold content.

One says 10k, one is from ireland and I can't read the writing cuz it is so small, one is striling silver, and the other says 10 k

Do they all cause the problem? If so, I would say that it is definitely not the rings. Especially if it is from silver and gold.

I looked this up and one chemist stated that gold will not cause a change in skin color. He stated that…”Gold is chemically rather inert. One of the other metals present (silver, nickel, copper) in the jewelry is probably causing the color change.”
That is why I heard that “cheap” jewelry can change the color of your skin - meaning that there is not so much gold in your gold rings.
He also went on to say that iron deficiency is not a cause.
http://antoine.frostburg.edu/chem/senese/101/misc/faq/gold-spots.shtml
http://www.corrosion-doctors.org/Implants/nickelallergy.htm#Gold
Also if your ring is white gold it is more likely that nickel is the cause as white gold is usually mixed with nickel as an alloy. Also if your body chemistry changes (hormones, perspiration, skin oils) it can cause you to be more sensitive to metals, especially something like nickel. That may be why sometimes your skin color changes and sometimes not.

I always thought if a ring turned your finger green it was because it was made of copper plated with another metal and when the gold/silver/platinum/titanium wore off the copper reacted with your sweat...

Even if it's not that i really doubt it's the iron thing as i personally have only ever had problems with very cheap rings (although these days i usually wear stone not metal) and as a young adolescent i was badly anaemic (low iron)

You could be right Bekaboo as copper is another alloy that is used in mixing with gold.