Interesting -- I've never thought about 0 = red, 60 = yellow, 120 = green, 180 = cyan, 240 = blue, 300 = purple as being user-unfriendly (simply because RGB is so much worse), but you make a good point.

What if CSS allowed hue to be defined as positions between any 2 adjacent options out of the 6 primitives defined by 60° increments?

E.g. bright orange could be either of:

  hsl(50% red yellow, 100%, 50%)
  hsl(50% yellow red, 100%, 50%)

While bright red-orange would be either of:

  hsl(75% red yellow, 100%, 50%)
  hsl(25% yellow red, 100%, 50%)

There's probably a more intuitive syntax to describe "25% of the way from red to yellow" that I can't think of.

And I think I'd be in favor of just six primitives. Using 30° increments would allow orange, but none of the other five positions have obvious names at all.