This is one theory that everyone is going on about and the one that I couldn't get out of my head during the summer holidays; the theory is that there exists of a group of gems that reign over Homeworld, known as the "Diamond Authority". There are a few instances when we hear about these gems; the most important one to me is when Jasper says "Yellow Diamond needs to see this" in the episode "The Return", another one is the strange symbol seen on the floor of the Gem Warship in "Jail Break"; the symbol is that of three triangles, one is blue, one is white and the other one is yellow. This seems to indicate that there are in fact three diamonds and not just one, but the big question remains...who are they?

My best guess is that each Diamond represents a different personality trait of the Gems themselves, Blue Diamond handles the military, Yellow Diamond is the political spearhead of the Gem Homeworld and White Diamond is the spiritual leader of the Gems. I imagine that each one of the Diamonds has their own powers and weapons to go with their occupations; as Blue Diamond would be mostly focused on offensive, White Diamond would be focused on defense while Yellow Diamond would be a perfect balance of both as she is the political leader of the Gem Homeworld and wouldn't go into battle unless she needed to or had to as a last resort. Another piece of evidence that they exist is in Jasper's clothing choice.

Have you ever noticed the Yellow Diamond symbol on Jasper's outfit? It seems to me that Yellow Diamond herself chose Jasper and Peridot to go to Earth after the events of "Marble Madness" where Peridot reported that there were gems still on Earth and those gems were members of Rose's Rebellion against Homeworld. It also makes me speculate that Jasper is in fact, Yellow Diamond's Bodyguard and the main reason for this speculation is Jasper's strength as shown in the series; on Homeworld, Yellow Diamond would need a strong gem to be her bodyguard and Jasper volunteered for this role, this is the one of the main reasons why she wears a yellow diamond on her outfit AS she's Yellow Diamond's servant like Peridot.