Platinum would be to polished aluminum what Sapphire would have been to Gorilla Glass:
visually unnoticeable while dinging the wallet in a very noticeable way. Both would look silver and
require you to verbally tell people that it's the platinum edition if you want to distinguish your watch from the multitudes of cheaper aluminum versions in the wild.
Gold will at least be obviously not aluminum, though, even there, gold electroplating the cheaper model would yield a visual effect very close to if not unnoticeable to the "real" gold model. I expect to see shops pop up offering to electroplate the aluminum version right away (much like the shops that can make Macbook aluminum pretty much any color you want)...
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