I would think so, I've seen reddish toning before. It is most likely
from the copper in the alloy.
--------------------------------------------------------------
I have a couple of slabbed $5 AGEs which exhibit the same orange-red toning the
OP writes of.
It is, as you posit, probably the copper in the alloy.
I have a First Spouse that has a similar blemish and I thought the first
spouse's were made of 24K and shouldn't have any copper being pure gold!