I(f your car came with the "gold" antifreeze, you should add only gold
antifreeze to maintain the added protection... after this many years, if the
cooling system hasn't been service properly, it wont matter, anyhow.

If you add green antifreeze to gold coolant, treat it as if it were all
green antifreeze. If you add red antifreeze to either green or gold coolant,
flush the system thoroughly and fill with your choice (preferably not red).

Once again, if the cooling system hasn't been serviced, it is long overdue
and the decision for which colour to add is moot.