So for my tool, I really need the live UI mockup without having to export first to tweak the colors until they work (e.g. often the off-white/very-light colors used for backgrounds are too vibrant otherwise), the control-point based curve editing helps to explore hue/saturation/lightness curves around a brand color without a lot of clicking, and I want the option for palettes where each color scale follows the same steps in lightness (for predictable contrast between steps from different color scales).

Barely any designers I work with know about P3 colors (feels like P3 mostly appeals to developers right now, for programmatic reasons?), so I'm not that interested in P3 if it means using OKLCH with its intimidating looking color picker. My tool uses HSLuv, which looks familiar like an HSL color picker, where unlike HSL only the lightness slider alters the WCAG contrast, so HSLuv (while limited to sRGB) is great for exploring accessible colors.

I've actually got support for APCA, but I find many struggle understanding WCAG contrast requirements already. There's Figma export too.

Anyway, there's lots of overlap between different color tools but the small details are important for different workflows and needs. I've started to realise too that most designers need a lot of introduction into building (accessible) color palettes in general so it's a tricky puzzle between adding features and trying to keep it simple, which is why I'm very open to suggestions!