I have two guesses as to what this means. Either it means simply higher resolution RGB encoding that describe more gradations of color OR they encode some type of color space information. RGB values describe a general color but it’s up to the device to determine precisely what shade of color to display. This way, different devices can choose a more precise color shade depending on the capabilities of the actual display hardware.

Regardless of the cables, LCD technology has a fundamentally worse color range than CRT and both of those have a worse color range than film, particularly in darks. No matter how you encode the signal you are limited by the actual display.