Hi anon, let’s have people add to this post! I’m so sorry, I moved so I don’t have all my books with me but my favorite description describing his demeanor as a whole is from Memnoch The Devil:
This was Armand. He sat on the stone park bench, boy like, casual, with one knee crooked, looking up at me with the predictable innocence, dusty all over, naturally, hair a long, tangled mess of auburn curls. Dressed in heavy denim garments, tight pants, and a zippered jacket, he surely passed for human, a street vagabond maybe, though his face was now parchment white, and even smoother than it had been when last we met. In a way, he made me think of a child doll, with brilliant faintly red-brown glass eyes-a doll that had been found in an attic. I wanted to polish him with kisses, clean him up, make him even more radiant than he was.
“That’s what you always want,” he said softly. His voice shocked me. If he had any French or Italian accent left, I couldn’t hear it. His tone was melancholy and had no meanness in it at all. “When you found me under Les Innocents,” he said, “you wanted to bathe me with perfume and dress me in velvet with great embroidered sleeves.”
“Yes,” I said, “and comb your hair, your beautiful russet hair.” My tone was angry. “You look good to me, you damnable little devil, good to embrace and good to love.”
-In Blood and Gold, Marius mentions that Armand’s facial features are slightly refined due to his Slavic blood
-In IWTV Louis mentions him with straight hair so I thought that was interesting
-He is considerably smaller than Lestat
-His eyes are big, glossy and expressive
-He has a very good poker face (Khayman didn’t know what he was thinking though he tried to probe his mind)
-Strong mental prowess that makes him very charming