A major historical flaw of the sRGB and HSL color models is that they are not perceptually uniform.
In HSL, pure blue at 50% lightness appears dramatically darker to human eyes than pure yellow at 50% lightness because human biology is far more sensitive to green and yellow wavelengths.
The modern OKLCH color model maps color according to human visual perception:
In OKLCH, a Lightness value of 0.70 delivers identical perceived contrast regardless of whether the hue is yellow, blue, or violet, making it the premier choice for algorithmic light/dark theme generators.
Level 2 · Elements of Design I