The color defined as yellow in the Munsell color system (Munsell 5Y) is shown at apex of color wheel. The "Munsell color system" is a color space that specifies colors based on three color dimensions: hue, value (lightness), and chroma (color purity), spaced uniformly in three dimensions in the elongated oval at an angle shaped Munsell color solid according to the logarithmic scale which governs human perception. In order for all the colors to be spaced uniformly, it was found necessary to use a color wheel with five primary colors—red, yellow, green, blue, and purple. The Munsell colors displayed are only approximate as they have been adjusted to fit into the sRGB gamut. The color that is called yellow in Pantone is displayed at right. The source of this color is the "Pantone Textile Paper eXtended (TPX)" color list, color #C, EC, M, PC, U, or CP—Yellow. The color yellow in Crayola crayons is displayed at right. Yellow was one of the original Crayola colors formulated in 1903. The color unmellow yellow is shown at right. The color "unmellow yellow" was formulated by Crayola in 1990. The color "unmellow yellow" is a similar fluorescent yellow to Laser Lemon but the color is brighter. In crayons, the color may appear slightly orange, though the computer display can appear more pale depending on one's monitor. The color is supposed to be fluorescent, but there is no mechanism to display fluorescence on a flat computer screen. Lemon is a color somewhat resembling yellow and named after the fruit. The color "lemon" is a representation of the color of the outer skin of a lemon. The first recorded use of "lemon" as a color name in English was in 1598. Maximum yellow was a Crayola crayon color from 1926 to 1944. The color mellow yellow is displayed at right. "Mellow yellow" was first used as a color name in English in 1948 when it was formulated as one of the colors on the Plochere color list. The source of this color is the "Plochere Color System", a color system formulated in 1948 that is widely used by interior designers. Donovan's album "Mellow Yellow", named after the song "Mellow Yellow", was popular during the Summer of Love in 1967. At right is displayed the color royal yellow. The color "royal yellow" is a representation of the color of the robes worn by the Emperor of China.