Loosely similar to CTCSS in the FM world, a form of repeater access control. Color has no relation to the term as it is numerical only
There are 16 codes available (0 to 15)
Generally, Color Code 1 is used by default in the ham world
PNWD tends to have fewer than a dozen that are not Color Code 1.
Client radios can be programmed to ignore received Color Code, similar to carrier squelch
Also known as Digital Monitor or Promiscous Mode