Board Thread:General Discussion/@comment-25539649-20150510212536/@comment-26812261-20150525171443

Seeing as how they specified "Yellow Diamond", and the emblem on the ship depicts a yellow, white, and blue diamond, it stands to reason that there are three diamonds, but that the Homeworld Gems only answer to one. My theory is that this is because the Blue and White Diamonds are trapped on Earth. Not only that, but we've already seen them.

The White Diamond being the powersource for the temple in Serious Steven, and the Blue Diamond being the gem animating the lighthouse in Horror Club. Reason being, the figures depicted in the temple are shown to have gems of roughly the same shape and size as these two in their chests.

Now in terms of their appearance, my theory is that only White and Yellow Diamond are depicted in the temple, and that the Moon Goddess Statue from Cheeseburger Backpack and The Test is modeled after Blue Diamond. Her association with the moon is viable due to the fact that, on the temple wall in Serious Steven, the gem who is presumably Yellow Diamond is associated with the Sun. Furthermore, the Moon Goddess Statue is depicted holding a gem at chest-level that happens to be identical in appearance to the one Steven found in the lighthouse.

Got this picture to compare/connect everything:

http://vignette3.wikia.nocookie.net/steven-universe/images/f/fb/Whatif.png/revision/latest?cb=20150427021534

Note the depiction of the sun behind the yellow gem on the temple wall, the similarity with which the white gem and the Moon Goddess Statue frame their gems with their hands, and the obvious similarities between the lighthouse gem and the small replica on the statue.

If this were to end up being true, what we would know about Blue Diamond's personality is that she seems fixated on broken friendships and betrayal, seen when she archived the falling out between Lars and Ronaldo (despite the fact that the personal pain Lars caused her when he carved his name happened way early in the recording), and the comment Sadie made about the gem lashing out because it felt hurt and trapped. Could imply that Blue Diamond was betrayed by someone, possibly the other diamonds.

It's all just speculation, of course, but as of now all those pieces fit.