Fix default value for color field in calendar events

aleksis/core/mixins.py

@@ -714,6 +714,10 @@ class CalendarEventMixin(RegistryObject):
     def value_link(cls, reference_object, request) -> str:
         return ""
 
+    @classmethod
+    def value_color(cls, reference_object, request) -> str:
+        return cls.get_color(request)
+
     @classproperty
     def valid_feeds(cls):
         """Return a list of valid feeds."""