Main thing is how to avoid the situation in the future, so that you don't have to worry about how to react. My response would therefore be, before going all in (or calling an all-in bet), ask for a count of how many chips the opponent has remaining. Then any improperly hidden high-denom. chips will be known to you (and yes, the black chip was improperly hidden, but I think the burden is on you to discover that - although, esp. in tournaments, dealers will sometimes ask players to stack their chips properly in that regard).
I've been burned in the same way, and also argued that the hidden