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
Rank in Judo by the other organization. Advanced "kyū" levels can be earned by both seniors and juniors (children under the age of about 16) and are signified by wearing belts of various colours other than black. The order of belt colours can vary from dōjō to dōjō, depending on the dōjō's organizational affiliation. For senior players, both the United States Judo Federation (USJF) and ) the United States Judo Association (USJA) specify six "kyū", as listed in the table. The USJA requires "Beginners" (not a kyū) to wear a white belt until they test for yellow belt. The USJA also recommends wearing