Feldgrau is a green–grey color. It was the official basic color of military uniforms of the German armed forces from the early 20th century until 1945 or 1989. Armed forces of other countries also used various shades of that color. Feldgrau was used to refer to the color of uniforms of the armies of Germany, first the Imperial German Army and later the Heer of the Reichswehr and the Wehrmacht.
Feldgrau of the Wehrmacht (Stalingrad 1942)
Service dress in Hellgrau (German Bundeswehr)
Austrian service cap in Hechtgrau (pike-grey)
Austrian uniform color
Prussian blue is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula FeIII4[FeII(CN)6]3. Turnbull's blue is chemically identical, but is made from different reagents, and its slightly different color stems from different impurities and particle sizes.
Prussian blue
The Great Wave off Kanagawa by Hokusai, an artwork that makes extensive use of Prussian blue
Prussian blue in a vial
Simulated powder x-ray diffraction profile for Prussian blue crystal, crystallographic direction annotated. Image generated using CrystalMaker software.