Black alert

Black alert signalled on a Discovery console

Black alert, otherwise known as alert condition black, was an alert signal used on the USS Discovery and the USS Glenn in 2256 to signify that the ship was operating its experimental spore drive. (DIS: "Context Is for Kings", "The Butcher's Knife Cares Not for the Lamb's Cry")

According to a throne room control panel shown at a Mirror Universe exhibition running concurrent with San Diego Comic Con 2018, the ISS Charon also used black alert. [1]