The best thing IMO about SD sand is that it's much cheaper to purchase than live sand pound for pound and it can be just as effective in a marine tank when seeded with "live" rock or sand.
The package does read "Southdown" on it and most packages I have seen are blue and red.
If you do a search you can find much more detailed information on SD on this forum.
I did read on someone's personal reef site that you actually should wash the SD before using it because when it's stored they spray some sort of oil mixture to keep the dust down while the pile of sand is being stored. I believe the person who had this on there site did e-mail the company that sells the sand so from now on if I use SD sand I'm going to wash it to be safe.
HTH,
Brian
FWIW I read the opposite about the sand being treated. I added mine without washing it and didn't get an oily film, or any problems, and that was 6 months ago.