niisonge,
I was going to suggest "heicha" before reading the rest of the postings. I guess we are all great minds! After reading the rest, I still think this is the best choice. As already mentioned, it has the advantage of being the (or at least "an") actual Chinese term,
I know one US vendor who is already using "dark tea" - I believe most or all of what he is calling that is fu tea.
Trying to re-claim "black tea" is totally a lost cause, and would only breed confusion.
I thought "fu tea" was a specific kind of heicha
D.