Every colour on this site is oklch(L C H) — lightness, chroma, hue. The reason
is that lightness in OKLCH is perceptual, so two colours with the same L look
equally bright to the eye. In HSL they do not: hsl(60 100% 50%) and
hsl(240 100% 50%) are both “50% lightness” and one of them is yellow while the
other is nearly black.
That makes a theme derivable instead of hand-picked. The whole palette here hangs
off one --neutral-hue, and the dark theme is mostly the same chromas with the
lightness ramp inverted.
It also makes dimming honest. Fading a node in a graph to 15% opacity keeps its hue and just moves it down the lightness ramp, so a dimmed cluster still reads as the same cluster.