hookdown, I doubt the screw-choke investment would be regained in a sale of your Citori. It wouldn't lower the value, just hard to get your $500ish back. Blueing turning to plum is not uncommon in older guns, a bit surprising on a 25 year old (but you may have a lot of miles on the gun).

If future sale of the A-5 is possible, keep your reciept from Browning for the refinish.