Thanks for looking, POCKET-CHANGE - @pocket-change. The Local Coin Shop Dealer, thinks the acid, in older coin albums & humidity, is one way. It can take years, even decades. Then there are “coin doctors,” that try artificial toning, with acids & electricity, in seconds. I'm guessing this ASE, tone is artificial, because of its flat coloring. I've seen videos of acid bath & quick shock method, took like one second, but coins' colors were flat & dull.

I wish I knew the secret to this one:

Every light angle gives the colors a different look.