It really depends on the material you're doing. There are about a thousand different varieties of "pot metal", and the exact elemental composition will depend how badly it will oxidize, if at all. In general, MOST airsoft pot metals will oxidize in to a dull and dark grey, but there are some will not, depending on the levels of lead, zinc, aluminum, and other impurities are present.
If you could point out specifically what kit you're referring to, somebody with more experience may be able to point out the success of what you're trying to attempt.
And for what it's worth, Zinc and lead will almost never hold up to ANY acid bath, so attempting any form of acid bath to a pot metal using such a composition will never survive the process of electro plating.
At most, you'll get a shiny lump of metal that doesn't resemble anything close to a gun.