ticker-serve/index: switch unknown calendar color from white to grey

ticker-serve/src/index.rs

@@ -50,7 +50,7 @@ fn group_by_day<'e>(config: &'e Config, es: &'e [Event]) -> Vec<DayEvents<'e>> {
                             let url = event.url.as_ref().map(|url| fix_url(url));
                             let color = config.calendars.get(&event.calendar)
                                 .map(|calendar| &calendar.color[..])
-                                .unwrap_or("white");
+                                .unwrap_or("grey");
                             (event, url, color)
                         }).collect(),
                 });