Argon is the Xbox 360 codename for the wireless controller RF and ring of light board. It is a board that plugs in to a port on the front of the Xbox 360 motherboard.
The Argon boards first appeared on early XeDK Beta kits. They used an earlier firmware that was incompatible with retail Xbox 360 wireless controllers. The ring of light firmware was also different on Beta XeDKs with the running animation being an endless rotating ring.
The primary Argon LED colors were green with the exception being the XNA XDKs which used blue LEDs.
Early Argon boards were flashed using an external Lamprey board.