The arcade I go to has AE2012 and on the idle game animation it shows the characters in alternate costumes, but I can’t seem to figure out how to choose them in-game. is it possible or just a joke Capcom is playing on arcade players?
We have the same deal here in Sydney. I believe the costumes are enabled as part of the underlying card system IV uses in Japan. The cards store your win/loss stats, Battle Points, player name, preferred colours and chosen costume.
Without the cards, the game defaults to the stock costumes and two colours. Its entirely possible these options can be enabled by way of cabinet dip switches and settings (much like how you enable/disable CPU Gouken/Oni/E.Ryu, or apply round allotment, time and difficulty settings) perhaps.