It must be retroreflective and/or equipped with alternately flashing red lights. The truck had been parked on double yellow lines with its hazard lights flashing. School crossings with flashing yellow lights remain. Some describe seeing one or more shimmering arcs of white or colored flashing lights. Other colors for flashing lights or beacons are not allowed. However, the lights are actually flashing. People who survive hanging report seeing flashing lights and hearing ringing sounds. Most LED lights will work in either flashing or steady modes. The active visual warnings are usually in the form of flashing lights. The performance featured a backing consisting of flashing lights and background dancers. This incarnation of the cave features a multitude of flashing lights, mostly in neon. They smile, with their right eye flashing red. Often, this is used in conjunction with a flashing siren. My lightning's flashing across the sky. Fire alarm panels indicate an abnormal condition via a solid or flashing LED.