Avoid inaccurately describing HSL as a "color space" (sass#504)

Closes sass#503

Author: Israel-4Ever

source/documentation/values/colors.html.md.erb

@@ -11,14 +11,14 @@ title: Colors
 
 Sass has built-in support for color values. Just like CSS colors, they represent
 points in the [sRGB color space][], although many Sass [color functions][]
-operate in the [HSL color space][] as well. Sass colors can be written as hex
-codes (`#f2ece4` or `#b37399aa`), [CSS color names][] (`midnightblue`,
-`transparent`), or the functions [`rgb()`][], [`rgba()`][], [`hsl()`][], and
-[`hsla()`][].
+operate using [HSL coordinates][] (which are just another way of expressing sRGB
+colors). Sass colors can be written as hex codes (`#f2ece4` or `#b37399aa`),
+[CSS color names][] (`midnightblue`, `transparent`), or the functions
+[`rgb()`][], [`rgba()`][], [`hsl()`][], and [`hsla()`][].
 
 [sRGB color space]: https://en.wikipedia.org/wiki/SRGB
 [color functions]: ../modules/color
-[HSL color space]: https://en.wikipedia.org/wiki/HSL_and_HSV
+[HSL coordinates]: https://en.wikipedia.org/wiki/HSL_and_HSV
 [CSS color names]: https://developer.mozilla.org/en-US/docs/Web/CSS/color_value#Color_keywords
 [`rgb()`]: ../modules#rgb
 [`rgba()`]: ../modules#rgba