Condition green refers to the normal operating condition (cruise mode) of a starship




yellow alert or condition yellow is the second highest alert signal status on Starfleet vessels, one stage below red alert. It designates a ship-wide state of increased preparedness for possible crisis situations.




Red alert" comes from the naval tradition of general quarters, and in fact the command "general quarters" may be used interchangeably to bring the ship into red alert. In TNG: "Where No One Has Gone Before", Captain Jean-Luc Picard issued both commands. The Klingon equivalent for red alert may be a reference to the American alert system DEFCON.

In ENT: "Singularity" it is hinted at that Lieutenant Reed had developed the term red alert, as it was jokingly referred to as "Reed alert". It was never mentioned again, but tactical alert screens all over the ship later displayed "Alert Condition Red". (citation needed • edit)
In VOY: "Scorpion, Part II", Chakotay mentioned that the USS Voyager would remain on "full" red alert. This may signify that there are multiple levels of red alert status, or that certain aspects of red alert, such as manning battle stations, can be stood down while allowing other aspects such as charged weapons to remain active. It may however simply refer to the fact that Voyager would remain at red alert for the duration.

In Star Trek VI: The Undiscovered Country, it can be heard that only certain decks should remain on red alert while in Klingon space. This makes it clear that only parts of the ship can be on red alert, while the rest of the ship drops to a lower readiness level.

In TNG: , the red alert lights change during the show's run. The first time red alert is heard, is TNG: "Encounter at Farpoint" , but the lights aren't flashing red. The first time the lights are seen flashing red is in TNG: "The Naked Now" , which have only the top and bottom part of the lights flashing. However, beginning from TNG: "Where Silence Has Lease" , the whole part of the lights flash. The next change the lights have is seen in TNG: "Man of the People" , where there is a longer period between when it flashes and when the sound is heard.