On Vision and Colors are, however, nonessential properties that differ according to the type of light-refracting substance that is used. The top of the upper image is violet. Below the violet is blue. The bottom of the lower image is orange. Above the orange is yellow. In this way, along with the white disk and the black background, four prismatic colors appear: violet, blue, yellow, and orange. This is in disagreement with Newton's claim that there are seven prismatic colors. As the upper image overlaps black, it is seen as violet. Where it overlaps white, it is seen as blue. As the lower image
School colors follows the rule of tincture from heraldry, but exceptions to this rule are known. Common primary colors include orange, purple, blue, red, and green. These colors are either paired with a color representing a metal (often black, brown, gray (or silver), white, or gold), or occasionally each other, such as orange/blue, red/green, or blue/yellow. Pairing two metals, such as black/white, silver/gold, and especially black/gold, is also a common practice. Finally, some American schools, in a display of patriotism, adopt the national colors of red, white, or blue. In an effort to further establish identity and promote a standard, many institutions