Docs: fix stale ScssDocs in colors and background utility pages (#42698)

Uncomment and repoint the ScssDocs references that predate the v6
color/theme refactor (they pointed at markers removed from
scss/_config.scss). Cross-link to the Color and Theme customize docs
instead of duplicating the $colors/$theme-colors Sass maps that are
already documented there in full.

Author: mdo

site/src/content/docs/utilities/background.mdx

@@ -83,33 +83,13 @@ In addition to the following Sass functionality, consider reading about our incl
 
 ### Sass variables
 
-Most `background-color` utilities are generated by our theme colors, reassigned from our generic color palette variables.
-
-{/*<ScssDocs name="color-variables" file="scss/_config.scss" />*/}
-
-{/* <ScssDocs name="theme-color-variables" file="scss/_config.scss" /> */}
+Most `background-color` utilities are generated by our theme colors, reassigned from our generic color palette variables. Grayscale colors are also available, but only a subset are used to generate any utilities. See the [Color]([[docsref:/customize/color]]) documentation for our base color variables and map.
 
 <ScssDocs name="variable-gradient" file="scss/_config.scss" />
 
-Grayscale colors are also available, but only a subset are used to generate any utilities.
-
-{/*<ScssDocs name="gray-color-variables" file="scss/_config.scss" />*/}
-
-Variables for setting `background-color` in `.bg-*-subtle` utilities in light and dark mode:
-
-{/* <ScssDocs name="theme-bg-subtle-variables" file="scss/_config.scss" /> */}
-
-{/* <ScssDocs name="theme-bg-subtle-dark-variables" file="scss/_variables-dark.scss" /> */}
-
 ### Sass maps
 
-Theme colors are then put into a Sass map so we can loop over them to generate our utilities, component modifiers, and more.
-
-{/* <ScssDocs name="theme-colors-map" file="scss/_config.scss" /> */}
-
-Grayscale colors are also available as a Sass map. **This map is not used to generate any utilities.**
-
-{/*<ScssDocs name="gray-colors-map" file="scss/_config.scss" />*/}
+Theme colors are then put into a Sass map so we can loop over them to generate our utilities, component modifiers, and more. See the [Theme]([[docsref:/customize/theme]]) documentation for the full `$theme-colors` Sass map.
 
 ### Sass mixins
 

site/src/content/docs/utilities/colors.mdx

@@ -110,21 +110,11 @@ In addition to the following Sass functionality, consider reading about our incl
 
 ### Sass variables
 
-Most `color` utilities are generated by our theme colors, reassigned from our generic color palette variables.
-
-{/* <ScssDocs name="theme-color-variables" file="scss/_config.scss" /> */}
-
-Grayscale colors are also available, but only a subset are used to generate any utilities.
+Most `color` utilities are generated by our theme colors, reassigned from our generic color palette variables. Grayscale colors are also available, but only a subset are used to generate any utilities. See the [Color]([[docsref:/customize/color]]) documentation for our base color variables and map.
 
 ### Sass maps
 
-Theme colors are then put into a Sass map so we can loop over them to generate our utilities, component modifiers, and more.
-
-{/* <ScssDocs name="theme-colors-map" file="scss/_config.scss" /> */}
-
-Grayscale colors are also available as a Sass map. **This map is not used to generate any utilities.**
-
-{/*<ScssDocs name="gray-colors-map" file="scss/_config.scss" />*/}
+Theme colors are then put into a Sass map so we can loop over them to generate our utilities, component modifiers, and more. See the [Theme]([[docsref:/customize/theme]]) documentation for the full `$theme-colors` Sass map.
 
 ### Sass utilities API