Hex Color Converter (HEX, RGB, HSL)

A hex color code is a base-16 encoding of three 8-bit channel intensities in the sRGB color space. Each pair of digits spans 00 to FF, that is 0 to 255, giving 256 levels per channel and 16,777,216 possible combinations. The shorthand form expands by doubling each digit, so the code F06 is exactly FF0066. Modern CSS also accepts four- and eight-digit forms in which the final pair encodes an alpha channel. RGB is a device-oriented model and a poor one for reasoning about color, which is why the same value is usually restated as HSL. Hue is an angle from 0 to 360 degrees around the color wheel, saturation expresses chroma from 0 to 100 percent, and lightness runs from 0 percent at black through 50 percent for the pure hue to 100 percent at white. CMYK is the subtractive model used in printing, and the conversion applied here is the naive algebraic one that ignores ink and paper behavior, so treat those values as indicative rather than press-ready. Relative luminance uses the coefficients 0.2126 for red, 0.7152 for green, and 0.0722 for blue, taken from the Rec. 709 primaries, reflecting that the eye is roughly three times more sensitive to green than to red. Luminance drives WCAG contrast ratios, which require 4.5:1 for normal text and 3:1 for large text at level AA. A strict WCAG calculation first linearizes each channel through the sRGB transfer function, so a weighted average of raw values is an approximation, not a substitute for a full contrast check.

The RGB triple predates the web by well over a century. James Clerk Maxwell demonstrated three-color additive photography in 1861, and the model later became the basis of color television and then of CRT computer displays. Hexadecimal notation reached web authors through early browsers: Netscape Navigator support for the bgcolor and text color attributes in 1994 and 1995 made six-digit codes the everyday vocabulary of web design. HTML 3.2, published by the W3C in January 1997, formalized both the RRGGBB syntax and sixteen named colors inherited from the standard VGA palette. Because much 1990s hardware ran in 8-bit indexed color, designers restricted themselves to the 216-entry web-safe palette, in which each channel used only the values 00, 33, 66, 99, CC, and FF. That constraint dissolved as 24-bit displays became standard. The sRGB space in which hex codes are now interpreted was defined by Hewlett-Packard and Microsoft in 1996 and published as IEC 61966-2-1 in 1999, giving the numbers a consistent meaning across devices for the first time. The HSL and HSV models were derived from earlier artist color systems and formalized for computer graphics by Alvy Ray Smith in a 1978 SIGGRAPH paper. CSS gained hsl() notation in the CSS Color Module Level 3, a W3C Recommendation in 2011, and later levels added wide-gamut spaces such as lab, lch, and oklch.