Wow...maybe one of AMD's plants ran out of polish and the new polish isn't the same colour?
Don't worry about it....the colour of polish on the core has nothing to do with anything.
For some time there was rumours floating around that the copper cores had a greenish tint, and the AL cores has a bluish tint, but that in fact turned out to be backwards, and it's unrelated the metals.
The Dresden fab used a polish with a bluish tint to it and the Texas plant uses a polish with a greenish tint to it.
Maybe one of the two ran out and is using a new kind of polish. If the CPU works ok don't worry about it.