This really surprised me. I inventoried a stash from years ago, found a 1/4 oz gold philharmonic from austria had a red spot on it. Small, but noticeable. On a 999 coin? This really surprised me. I've seen red spots on 22 carat coins, like krugs, but never expected a spot on a 999.9 coin.
At the time, I bought two of them from a very respectable online dealer. The other coin was fine. Both are beautiful coins, strikingly.