The three gems in charge are three diamonds; Yellow, White, and Blue.

This was in the ship in Jail Break, and shows a pyramid composed of three triangles; yellow, white, and blue.

Before they got on the ship, Jasper wants to refer to Yellow Diamond about Steven, so we know she actually exists.

Now, we’ve definitely seen these gems before, in Serious Steven:

The Diamond Authority seem to have triangles instead of diamonds, like every other Homeworld gem: the triangle could be a sign of leadership and authority. 

So if we’re going by power, then White should be the diamond in charge, right? because they’re at the top of the pyramid? 

So why is Rose fighting Blue, and why does Jasper want to refer to Yellow Diamond?

Because these three gems rule individually, and not as a whole:

Both Peridot and Jasper have yellow diamonds on their outfit, and Lapis has a blue. Peridot and Jasper would therefore listen to Yellow and take commands from her; she is the one who sent them to earth to restart Kindergarten. 

Homeworld is lead by three separate leaders - Blue Diamond, Yellow Diamond, and White Diamond - and Yellow Diamond wishes to restart Kindergarten.

Since Blue is seen fighting Rose, and Yellow wishes to restart Kindergarten, We can hope that White is a good gem.