Color Palette Generator

Color harmony schemes are geometric rules applied to the hue axis of the HSL cylinder, where hue runs 0 to 360 degrees, saturation 0 to 100 percent, and lightness 0 to 100 percent. A complementary pair sits 180 degrees apart, triadic colors at 120 degree spacing, analogous colors within 30 degrees of the base, split-complementary at 150 and 210 degrees, and tetradic at 90 degree intervals. Monochromatic sets hold hue and saturation fixed and step lightness, typically across a 20 to 80 percent band so the darkest and lightest steps remain usable for text and backgrounds. Holding saturation and lightness constant while rotating hue is what makes the output feel like a set rather than a collection. The accessibility figures come from a separate model. WCAG relative luminance is 0.2126R plus 0.7152G plus 0.0722B computed on linearized sRGB channels, where values at or below 0.03928 are divided by 12.92 and the rest are raised to the 2.4 power after the 0.055 offset. Contrast ratio is then (L1 plus 0.05) divided by (L2 plus 0.05), spanning 1:1 to 21:1. Level AA needs 4.5:1 for body text and 3:1 for large text at 24px regular or 18.66px bold; AAA needs 7:1. The main caveat is that HSL is not perceptually uniform: yellow at 50 percent lightness looks far brighter than blue at the same value, so a hue rotation at fixed lightness can produce swatches of very unequal visual weight. CIELAB or OKLCH give more even results.

The circular arrangement of hues begins with Isaac Newton, who bent the spectrum into a closed circle in Opticks in 1704 so that the non-spectral purples could join red to violet. Moses Harris published the first full-colour printed wheel in The Natural System of Colours around 1766, and Goethe followed with Zur Farbenlehre in 1810. The most consequential figure for practical palette work was Michel Eugene Chevreul, director of dyeing at the Gobelins tapestry works in Paris, whose 1839 treatise on the law of simultaneous contrast explained why adjacent complements intensify each other, a finding that fed directly into Impressionist and Neo-Impressionist painting. Systematic three-dimensional colour notation arrived with Albert Munsell, whose A Color Notation of 1905 separated hue, value and chroma on measured scales. Johannes Itten taught a twelve-part wheel and a set of colour contrasts at the Bauhaus in the 1920s, which is the direct ancestor of the complementary, triadic and analogous vocabulary designers still use. The digital form came from Alvy Ray Smith, who presented HSV and the related HSL transform at SIGGRAPH in 1978 as a more intuitive front end to RGB hardware. CSS gained the hsl() notation through the CSS Color Level 3 work of the 2000s. The contrast ratio formula used here was introduced in WCAG 2.0, published as a W3C Recommendation in December 2008, and carried forward unchanged into WCAG 2.1 in June 2018.