A Fallen Angel that has aged (eg, is 80 years old and looks it) who turns to darkness due to the fear of death, will find once again they are young and beautiful – although darkly so. 

Appearance
They all have wings (unless they lost them when they were Fallen Angels). Their wings are either black or red.

Their hair colouring is the same as it was when they were Fallen.

Dark Angels have a dark aura. Not a halo, just a dark or black radiance, as though they are living in a stormcloud.

Well defined muscles or athletic in build, as the magics that created them to darkness also offered them strength through physical mastery, to enhance Vanity.

Magical Talents
Dark Angels have mild glamour - they can 'hide' their wings magically.

Dark Angels can harm others with a single touch (via cursing them). This would be a scalding touch, or a touch of pestilence. They cannot immediately kill with their touch, just harm.

Very strong physically, whether they look it or not

Artwork: Alath'Erna, Angel of Destruction [Website]