Colour Tool
Every colour space CSS understands, WCAG 2 and APCA contrast side by side, perceptual scales built in OKLCH, and a palette designed for OLED screens where black really is off.
Built in OKLCH, so each step is an even perceptual distance apart rather than an even numeric one. Chroma is eased at the ends to stop the lightest and darkest steps looking muddy.
How this colour reads to the most common forms of colour blindness. If two colours in your palette collapse into one here, they cannot be the only thing carrying meaning.
On an OLED screen a black pixel is switched off: it costs nothing and has effectively infinite contrast. That makes true black tempting, but large areas of it can smear while scrolling and make dark greys crush together. These surfaces carry a trace of your hue instead, which is what most dark interfaces actually do.
Conversions follow CSS Color 4, with Lab and LCH on the D50 white point and OKLab and OKLCH on D65, as the specification requires. OKLab is Björn Ottosson's work. The WCAG 2 ratio is the relative-luminance formula from WCAG 2.2; the Lc figure is APCA, drafted for WCAG 3 and not yet a legal standard, shown alongside rather than instead of it. Colour-vision simulation uses the Viénot–Brettel–Mollon matrices. CMYK has no colour profile behind it, so treat it as an approximation and trust your printer's proof instead.