To dream of a knight represents an aspect of your personality that is loyal or defends good virtues. It symbolizes honor and protection from darker aspects of your life. Something that keeps you on the straight and narrow.
A black represents an aspect of personality that is loyal to bad intentions or negative habits. A part of your personality that wants to stay negative and never resist it.
Example: A young man dreamed of seeing protect a castle entrance. In waking life he was forced to spend a month living with relatives he considered to be bad influences. The reflected his attempt to protect his values by resisting his relatives bad influences.