Hard Boiled Egg Green Ring

I can't avoid Hard Boiled Egg Green Ring no matter what I do. Is it me or is it the egg? Why most of the time there is this greenish ring around the yolk of  my hard boild eggs? What am I doing wrong? 

I tried getting fresh eggs to no avail, talked to the people at the market they had no idea and now I turn to you the cooks busy in the kitchen you must have an idea. Please help?

ANSWER

The discoloration that sometimes we notice around hard boiled yolks results from a reaction between iron in the yolk and sulfur in the egg white. This happens when the eggs are boiled at too high temperature for too long. 
 
When you get hard boil egg green ring color formed around the yolk, don't throw them away. although unsightly, the eggs are still perfectly harmless to eat. In order not to allow the ring around the yolk to form follow the instructions here.
 
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This question was by Jack2010 and answered by Mariette