diff --git a/docs/guidelines.md b/docs/guidelines.md
index 39006a9683..c82bab8ad3 100644
--- a/docs/guidelines.md
+++ b/docs/guidelines.md
@@ -108,7 +108,7 @@ Make use of `<thead>`, `<tfoot>`, `<tbody>`, and `<th>` tags (and `scope` attrib
 
 ### Formatting
 
-* Use hex color codes `#000` unless using `rgba()`.
+* Use hex color codes `#000` unless using `rgba()` in raw CSS (SCSS' `rgba()` function is overloaded to accept hex colors as a param, e.g., `rgba(#000, .5)`).
 * Use `//` for comment blocks (instead of `/* */`).
 * Avoid specifying units for zero values, e.g., `margin: 0;` instead of `margin: 0px;`.
 * Strive to limit use of shorthand declarations to instances where you must explicitly set all the available values.