feat(Util): add missing colors to docs (#3843)

Co-authored-by: Crawl <icrawltogo@gmail.com>

src/util/Util.js

@@ -419,6 +419,10 @@ class Util {
    * - `DARK_GREY`
    * - `LIGHT_GREY`
    * - `DARK_NAVY`
+   * - `BLURPLE`
+   * - `GREYPLE`
+   * - `DARK_BUT_NOT_BLACK`
+   * - `NOT_QUITE_BLACK`
    * - `RANDOM`
    * @typedef {string|number|number[]} ColorResolvable
    */