I think you were very lucky to get one of the purple $5. You may be correct - purple centers may be the standard for the $100 GOs - I have not seen any with black centers - in fact I have not seen any others at all. The only reason I thought they might be an error is the way the purple runs into the lettering in the Thunder Valley logo. In the black $5 and $25 the lettering is a nice crisp white and I would have thought they would have wanted it to be the same way on the $100. May be one of those mysteries we'll never know the straight story on...