I'm not 100% sure, but I believe that the castle would fly the king's banner, and the liege's banner as well. The kings would be flown at the highest position, and the Liege banner would be below it. There might also be lesser banners if knights or other nobles were visiting or in residence. These would, I believe, be hung on the walls in the feasting room or on small poles in the courtyard.

Talent is God's gift to you. Using it is your gift to God.