Cobalt blue
Cobalt blue in impure forms had long been used in Chinese porcelain, but it was independently discovered as a pure alumina-based pigment by Louis Jacques Thénard in 1802. Commercial production began in France in 1807. The first recorded use of "cobalt blue" as a color name in English was in 1777. The leading world manufacturer of cobalt blue in the 19th century was Benjamin Wegner's Norwegian company Blaafarveværket ("blue colour works" in Dano-Norwegian). Germany was also famous for production, especially the blue colour works ("Blaufarbenwerke") in the Ore Mountains of Saxony.
Emergency vehicle lighting
The use of the blue emergency light originates in Germany during World War II. As a result of the ‘Verdunkelung’, a measure for aerial defense from 1935, cobalt blue was regulated to replace the red color used until 1938 in emergency vehicle lights. Due to the scattering properties of the blue color, it is only visible to lower altitudes and is therefore less easily spotted by enemy airplanes.