How to detect theme in sage crm 7.3

As everyone aware that Sage CRM 7.3 has new and improved theme but if system is upgrading from Sage CRM 7.2 to Sage CRM 7.3 the older themes will still be present and still available and the new theme is just an option. so my question is, During installation of add-on is there any workaround to detect which theme is currently applied on Sage CRM 7.3 ?