Color theory primary colors work at all is that the imperfect pigments being used have sloped absorption curves, and thus change color with concentration. A pigment that is pure red at high concentrations can behave more like magenta at low concentrations. This allows it to make purples that would otherwise be impossible. Likewise, a blue that is ultramarine at high concentrations appears cyan at low concentrations, allowing it to be used to mix green. Chromium red pigments can appear orange, and then yellow, as the concentration is reduced. It is even possible to mix very low concentrations of the blue mentioned and
Orange (colour) of extremes, trying to make the colours intense, and not a harmony of greys." In the 20th and 21st centuries, the colour orange had highly varied associations, both positive and negative. The high visibility of orange made it a popular colour for certain kinds of clothing and equipment. During the Second World War, US Navy pilots in the Pacific began to wear orange inflatable life jackets, which could be spotted by search and rescue planes. After the war, these jackets became common on both civilian and naval vessels of all sizes, and on aircraft that flew over water. Orange was