"Blue Sky" is the name of an underground drug marketplace. It is one of the new[1] sites looking to replace Silk Road and is apparently popular.

Onion link:

http://blueskyplzv4fsti.onion/

edit: screenshot of the market homepage:

http://imgur.com/O9fvlxI.png

[1] turns out it was launched in the first week of December, which makes it nearly 3 months old - enough time to get it noticed and flagged by the us.gov.