A demonstration
Ten colors, one OKLab lightness. Drag the hue and watch their real lightness—and whether text survives on them—come apart at the seams. Then flip the ruler to CIE L* and watch the chaos snap into line.
Every swatch is a real, maximally-saturated sRGB color at the chosen lightness — click the hex to copy it into any contrast checker. Verdicts use WCAG 2.x relative luminance at the 4.5:1 AA threshold for normal text; APCA runs on the same luminance and tells the same story. The spread you see is a chroma effect: at zero chroma every hue collapses to one gray, so this is what happens the moment you build a saturated ramp. The Helmholtz–Kohlrausch effect (saturated colors reading slightly brighter than luminance predicts) is real and modeled by neither ruler — but it doesn't change which text passes. Companion to the L* Contrast Meter.