“HSL” is a trivial transformation of RGB. It’s what you get when you prop an RGB cube up on one corner, squish 6 of the other corners into the same plane, and then inflate it until it fills a cylinder shape. (Note that none of these steps make any reference to human perception.) Here’s my 2010 diagram showing that visually https://en.wikipedia.org/wiki/File:Hsl-and-hsv.svg

> Also, how exactly is lab color useful in web programming? How do you support it in CSS or HTML?

Implementing CIELAB in Javascript is straightforward. https://github.com/jrus/chromatist/blob/master/src/cielab.co...

You could alternately use a model like CIECAM02, but that gets a whole lot more complicated. https://github.com/jrus/chromatist/blob/master/src/ciecam.co...