In my opinion the Helm of Darkness should be black, however the main function of the helm is to make things invisible so the question is difficult to answer.
The Cyclopes forged Hades' helmet
The cyclops had made it for Hades.
none hades does not have a symbol
The Helmet of Darkness.
He made Hades a helmet that could make him invisible.
the cyclops gave hades a helmet/mask
yes
Cerberus, helmet of invisibility
The Helm Of Darkness
The cyclopes made it for him
Hades weapon of choice is a helmet which turns the wearer invisible.
Hades' symbol, the Healm of Darkness also known as the invisible helmet was a helmet made for Hades by the Cyclopes. It is his symbol of power. It can make fear so intense that it can stope your heart.