Many Blu-Ray players today offer the option of transmitting the video data using Deep Color. Blu-Rays are encoded with 8 bit data for each color so no additional detail will be created with this option so why is it present?
I have found activating 10 or 12 bit data for each color can degrade the image. When this feature is activated the data rate will increase dramatically potentially exceeding the cable capacity. The other thing that can happen is the data is incorrectly converted to the higher bit rate or it is improperly handeled in the source.
When you must alter the signal in the player with something like brightness or contrast that is a situation where deep color may help. This will only be true if the display fully supports more than 8 bit color data. Unfortunately, if you obtain the detailed design information you will find that many displays that accept a deep color input will just drop any data over 8 bits.