use textColorOnPrimaryBackground

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

app/src/main/res/layout/controller_chat.xml

@@ -133,6 +133,6 @@
         app:pb_backgroundColor="@color/colorPrimary"
         app:pb_icon="@drawable/ic_baseline_arrow_downward_24px"
         app:pb_text="@string/nc_new_messages"
-        app:pb_textColor="@color/white" />
+        app:pb_textColor="@color/textColorOnPrimaryBackground" />
 
 </RelativeLayout>