HUSL is a color space that is perfect for programmers that want to choose colors dynamically for their program.
Compare Blue to Yellow. In the Hue-Saturation-Value space, both have a “saturation” and “value” of 100. But the yellow is clearly closer to white than the blue is, since I can’t actually read yellow on white. (This is used to identify color laser printers without significanly affecting the appearance)
In HUSL, the luminance sets how bright any of the colors in the hue-saturation plane appear. In my case, I use a default luminance of 50%, and a saturation of 100%. Hue is what I change, advancing by 1 degree in hue per step of the wallpaper.