Black Dragons are a liability, as they could break down to the Old Gods' whisper anytime (as shown in lore), and thus breaks the whole ideal about Heartwing being a family.
I am sorry to say that Adiastrasza is right in this case, we do not allow black dragons.
[Alive] Aerenstrasz - Leader of Heartwing
[Alive] Aerdranstrasz - Child of Aeren
[Alive] Azraelstrasz- Second son of Asherystrasz - Not part of Heartwing
[Deceased] Asherystrasz - Retired leader of Heartwing
[Deceased] Hydrastrasz - Former Leader of Heartwing