StandardHSL

StandardHSL is a proposed specification for expressing colors using the Hue–Saturation–Lightness (HSL) color model. It seeks to harmonize the representation, parsing, and conversion of HSL colors across software, web platforms, and design workflows, thereby improving interoperability and reducing ambiguity in color handling.

The core of StandardHSL specifies three components: hue, saturation, and lightness. Hue is defined as a degree value from 0 to 360, with values wrapping modulo 360. Saturation and lightness are expressed as percentages from 0% to 100%. An optional alpha component allows transparency and is defined on a scalar range from 0 to 1. The textual syntax is hsl(H, S%, L%) or hsla(H, S%, L%, A), where H may be any real number and is normalized, S and L are clamped to [0, 100], and A is clamped to [0, 1].

Conversion to RGB follows a formal algorithm. Given H, S, and L, the model computes intermediate values to produce red, green, and blue components in the 0–255 range. This enables consistent rendering on devices using sRGB and supports cross-system color management. StandardHSL also defines rounding rules, handling of edge cases (such as grayscale colors with zero saturation), and guidance for precision in serializations.

Status and usage indicate that StandardHSL remains a draft in standardization discussions and has not been universally adopted by major standards bodies. Some design tools and libraries offer implementations aligned with its rules or compatible behaviors with existing CSS hsl representations. The standard is intended to complement, not replace, perceptual color spaces and device-specific color workflows. See also HSL, CSS Color, and perceptual color models.