add note about how to learn about color (#1929)

* add note about how to learn about color

* Apply suggestions from code review

Co-authored-by: Inayaili León <yaili@github.com>

Co-authored-by: Inayaili León <yaili@github.com>

Author: ashygee

docs/content/utilities/colors.mdx

@@ -8,7 +8,7 @@ status: Beta
   Please note Primer CSS v18 has changed the naming of these color classes. Check the <a href="/css/support/v18-migration">migration guide</a> to make sure your app is up to date.
 </Note>
 
-Use color utilities to apply color to the background of elements, text, and borders.
+Use color utilities to apply color to the background of elements, text, and borders. These utilities should only be used where color is not provided by a component. To learn more about how to apply color, read the [color documentation](https://primer.style/design/foundations/color) in the [interface guidelines](https://primer.style/design/).
 
 ## Text