[Note: The following is a mail sent to Les Dabel, of Dabel Brothers Productions, as part of their preparation for adapting an excerpt from "The Sworn Sword" in the second edition of the Hedge Knight graphic novel. Included at the end is a follow-up.]
Do you have LEGENDS II? There's a detailed description of Bloodraven, aka Lord Brynden Rivers, in "The Sworn Sword." He is the most distinctive of the three, an albino with a red winestain birthmark on his neck and cheek that looks (vaguely) like a raven in flight.
Daemon Blackfyre and Bittersteel, aka Ser Aegor Rivers, are both bastard sons of King Aegon IV (the Unworthy), although Daemon is Targ on both sides, while Bittersteel's mother was a Bracken. Bloodraven is also the king's bastard, by yet another mother.
At the time of the Redgrass Field, Daemon Blackfyre was 26, and his twin sons Aegon and Aemon, who squired for him, were 12. Bittersteel was 24, and Bloodraven 21. This was about thirteen years before "The Hedge Knight." Daemon was very much a Targaryen, albeit bastard born. He had the silver-gold hair, the purple eyes. He looked heroic; tall, muscular, handsome, wide shoulders, flat stomach. A great warrior. Clean-shaven, wears his hair long, like Marvel's Thor. Can be charming and charismatic too, with a winning smile. He used the arms of House Targaryen on his battle standards, but with the colors reversed: a black three-headed dragon on a red field. He'd bear the same sigil on his shield. I can imagine him in gorgeous, ornate plate armor, red and black, black dragon wings sprouting from his helm.
Bittersteel is also imposing in appearance, but since his mother was not a Targ, he does not have the coloring. He has the purple eyes, but his hair is black. A close-cropped beard, hardly more than a shadow. Somewhat of a Conan look to him; not the Frank Frazetta Conan, and definitely not the Arnold Conan, but more the Barry Windsor-Smith Conan, lean and lithe and hard. And angry. Handsome in a dark brooding way, but pissed off at his bastard's lot in life. No smiles here. No-nonsense grey steel armor with a horsehead crest on the helm. His white shield has a grey longsword displayed bendy sinister, with a black dragon's head above and a red horse's head below, both facing out.
Bloodraven is described in "The Sworn Sword," so I won't repeat that here. He's tall and wiry, but sscrawny compared to his magnificent half-brothers. Although a good swordsman, his main weapon is the bow; he has a tall longbow made of weirwood, and fires white weirwood arrows fletched with raven feathers. He is also, by repute, a sorcerer. Sharp features, vaguely sinister.
Also, Bloodraven and Daemon Blackfyre wield swords of Valyrian steel, as does Ser Gwayne Corbray of the Kingsguard, also prominent in the battle.
You did not have to draw any Valyrian blades in "The Hedge Knight," but now you're got a plethora, it seems. They all have certainly similarities -- the color ranges from smoky grey to almost black, the ripples in the steel -- but each one is unique as well. Bloodraven carries Dark Sister, Corbray has Lady Forlorn, and Daemon fights with Blackfyre, the sword of Aegon the Conquerer and all the Targaryen kings that followed him.
Blackfyre should be somewhat larger and darker than the other two, and its design needs to suggest flames.
Don't bother working up those arms for Bittersteel, I've already changed them. Came up with a much cooler image...
So here's Bittersteel: a winged red stallion on a golden field. Only the horse has big black dragon wings instead of the usual Pegasus-style feathered angel wings, and he's snorting fire.