Collar Colors:
Leather/Brown - New Slave in Training, not broken-in yet and is contained in the cells in the basement area.
Black - Beginner Slave, works the common area in the front foyers
Green - Castle Slave, works all the upper common areas, like hallways and bathrooms, guest rooms, the dining area, etc.
Yellow - Nobles Slave, long-term guests and other royalty friends and company
Red - Duke/Duchess Slave, the lower level of royalty
Blue/Pink - Princes/Princess Slave, takes care of the general needs of princess and prince in their quarters.
Personal slaves get personalized collars, such as if a prince has a specific personal slave, the Queen's personal slave, King's personal slave, etc. The royal individual has a collar made just for their slave.