In the ruthless routes where Asterion gets gored, in his sprites, you can only see red stains, and none of the black ichor. Potential theory-breaker, oversight, or intentional design.
I'd rather not confirm or reject any theory but on this case I can tell you that there were "lore details" I thought of including on that sprite that ultimately weren't implemented because drawing it was not nice in any shape or form and I consider that sort of stuff mentally harmful. I didn't want nanoff to put any more time on it than necessary, we aren't Naughty Dogs.