There's a better one here ~
Galaxy S4 In-Depth First Impressions *Samsung Unpacked 2013* - YouTube
Look especially at 1:28 where the reviewer gives a meaningfull explanation of all the radios at the top of the handset and at 2:50 they then show and mention the RGB LED.
I still though have not found anything further on whether or not this LED can do separate colours for SMS like GoSMS does.
I know believe my source to be incorrect.