The Rainbow Codes were a series of code names used to disguise the nature of various British military research projects. They were mainly used from after the Second World War until 1958, when they were replaced by an alphanumeric code system.
Each rainbow code name was constructed from a randomly selected colour, plus an (often appropriate) noun taken from a list.
The colours used were:
- Black
- Blue
- Brown
- Green
- Indigo
- Jade
- Orange
- Pink
- Purple
- Red
- Violet
- Yellow
More information, including a list of code names on the Wikipedia page [1].