Define the face `org-agenda-calendar-daterange'

* etc/ORG-NEWS: Announce the introduction of the new face
  `org-agenda-calendar-daterange'.
* lisp/org-faces.el: Define the face `org-agenda-calendar-daterange'.
* lisp/org-agenda.el (org-agenda-get-blocks): Apply the face
  `org-agenda-calendar-daterange' to entries with a date range.

etc/ORG-NEWS

@@ -55,6 +55,11 @@ document header:
 ,#+LATEX_HEADER: \DefineVerbatimEnvironment{lstlisting}{Verbatim}{...whatever...}
 #+END_src
 
+*** New face: ~org-agenda-calendar-daterange~
+The face ~org-agenda-calendar-daterange~ is used to show entries with
+a date range in the agenda.  It inherits from the default face in
+order to remain backward-compatible.
+
 * Version 9.6
 
 ** Important announcements and breaking changes

lisp/org-agenda.el

@@ -7110,7 +7110,7 @@ scheduled items with an hour specification like [h]h:mm."
 		(throw :skip t))
               (setq face (if (= d1 d2)
                              'org-agenda-calendar-event
-                           nil))
+                           'org-agenda-calendar-daterange))
 	      (setq marker (org-agenda-new-marker (point))
 		    category (org-get-category))
               (setq effort (save-match-data (or (get-text-property (point) 'effort)

lisp/org-faces.el

@@ -660,6 +660,10 @@ month and 365.24 days for a year)."
   "Face used for agenda entries that come from the Emacs diary."
   :group 'org-faces)
 
+(defface org-agenda-calendar-daterange '((t :inherit default))
+  "Face used to show entries with a date range in the agenda."
+  :group 'org-faces)
+
 (defface org-agenda-calendar-event '((t :inherit default))
   "Face used to show events and appointments in the agenda."
   :group 'org-faces)