Perceptual Color Picker is the only open-source color tool that works with friendly color spaces, i.e. suitable for human vision. If you agree that a color gradient is a line between two colors, you’re good to go because it uses 3d geometry in color space to provide consistent color palettes.
Perceptual Color Picker use a background to display different color plans from perceptually uniform color spaces. The third coordinate which is not in the plane define it in the colors volume. It can vary with slider as a constant or as a gradient. Upon this background you can use different graphic tools i.e. segment, spline, polygon, related or palette to choose set of colors. Colors coordinates can be display in CIE Lab, CIE LcH, WEB, sRGB code. You can snapshot the whole user interface or just the color palette with coordinates as png file. You can also save in the clipboard the web codes.
The 1.1.0 version of perceptual color picker use JzAzBz color space of Pr. Ming Ronnier Luo who has received the 2017 International Association of Color - AIC Judd Award.