Alert Status
Ship's Status
Federation Starships have been devising means to call for different levels of alertness from their crews depending on a given situation since before the founding of the Federation. The earliest Earth starships used systems similar to that world's navies- "General Quarters" was a state of heightened readiness when the vessel was in danger or in combat. But the system did not ultimately carry over to the Federation.
Instead, Starfleet implemented a system that used the three primary colors in the visible spectrum, those that most Humanoid species would be able to perceive. By far the most common of these are Condition Yellow and Condition Red. Less often used as Condition Blue, Condition Gray, and the so-called "Black Alert."