In a post today on the Windows Blog, Microsoft has officially stated that Windows "Blue" will officially be called: Windows 8.1.
A preview for Windows 8 and Windows RT will be available starting on June 26th, the same time as the Build developer conference in San Francisco.
Full information here: Windows Keeps Getting Better
It's also being reported that Windows 8.1 will be available for free to current Windows 8 and Windows RT customers. So, if you were in that early adoption crowd, you can rest easy, knowing that Windows 8.1 will be available for you from the Windows Store later this year.
Mary Jo Foley suggests that Windows 8.1 will hit RTM sometime in August 2013.
Read Mary Jo's update here: Microsoft confirms Blue to be free for existing Windows 8 users