An enhancement can be played on any Hero in battle. If you have a blue and a silver Hero in battle, you can play blue or silver enhancements. If one Hero is removed from battle (by being discarded, captured, converted, etc.), then the other Hero remains in battle. The enhancements that no longer match a brigade are then discarded, but not negated (so their */* abilities won't add to the other Hero, but any special abilities aren't undone).
