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) series, wear orange swimsuits to make them stand out. Orange astronaut suits have the highest visibility in space, or against blue sea. An aircraft's two types of "black box," or flight data recorder and cockpit voice recorder, are actually bright orange, so they can be found more easily. In some cars, connectors related to safety systems, such as the airbag, may be coloured orange. The Golden Gate Bridge at the entrance of San Francisco Bay is painted international orange to make it more visible in the fog. Next to red, it is the colour most popular for extroverts, and as