Add color support

You can change the default color by changing the props (.props file for
the filesystem storage backend).

radicale/ical.py

@@ -434,6 +434,14 @@ class Collection(object):
         with self.props as props:
             return props.get("D:displayname", self.path.split(os.path.sep)[-1])
 
+    @property
+    def color(self):
+        """Collection color."""
+        with self.props as props:
+            if "A:calendar-color" not in props:
+                props["A:calendar-color"] = "#5ba209"
+            return props["A:calendar-color"]
+
     @property
     def headers(self):
         """Find headers items in collection."""