HSL and OKLCH are both ways to describe colors in CSS, but their coordinates mean different things. HSL is familiar and convenient for choosing a hue. OKLCH uses lightness, chroma, and hue in a perceptually oriented color space, which can make tonal adjustments more predictable across different hues.
Why the same HSL lightness can look uneven
HSL lightness is not perceptually uniform: setting two hues to the same percentage does not make them appear equally bright. If you build a palette by changing only HSL lightness, one hue may look much stronger or weaker than another. OKLCH lightness is designed to track perceived lightness more closely, though it does not remove every design judgment.
Adjust an OKLCH color in CSS
:root {
--brand: #7357e8; /* fallback */
--brand: oklch(55% 0.19 286);
--brand-soft: oklch(90% 0.06 286);
}Browsers that understand the second declaration use it; older browsers keep the preceding HEX value. Check the selected color on the displays and browsers you support, especially when using colors outside the sRGB gamut.
When to choose each format
Use HSL when its controls make a simple adjustment easy, when working in an existing HSL palette, or when a project expects that format. Try OKLCH when generating consistent lightness steps, comparing multiple hues, or defining a modern CSS theme. You can keep a HEX fallback and inspect the rendered result rather than assuming a coordinate change will preserve the exact appearance.
The CSS Color Module Level 4 defines the oklch() notation. Use the online color picker to inspect color values in multiple formats.