You meant the "Overlay" (bottom-left) to have HSL option too? Btw, if you open an issue/request with the right context, Saneef will look into it. I will nudge him if that makes sense.
Yes, so if I start a palette at Lightness 100 and end at Lightness 0, I should see these numbers in the resulting colors
In this specific example the starting color is still not ff, but f9 due to some easing interference (though I'd expect a function x=0 y=0 to not do anything for the very first color), but even then you still see a clear connection, and if you had 10 steps you'd see ~10 lightness point increase in each palette color
https://github.com/saneef/color-color