How would I know if a saffire ring is genuine, the gold band has dia, and a tiny inscription which I can't read. I wore the ring once since purchasing it the other day on line and my finger went green/black after an hour

Real gold does not make your hand change color.

Also should be obvious from price you paid.

You can take it to a store and ask

If the band is not real gold (your finger would not have changed colour) then you can almost bet the saphire is not real either. How much did you pay for it on line ?