Have the most boring reference sheet of the bunch, Grey Agate's.
Great Agate was supposed to be white for, well, White Diamond, but he came out off-coloured and a bit out of shape, so he was thrown out. In the end, the Crystal Gems picked him up, along with another character, and because of his natural high-ranking soldier instincts, he lead a squad of gems on a bunch of missions, which went pretty well. So, when Rhodochrosite died, he was the pretty obvious choice for de-facto leader of the Crystal Gems. This really stresses him out, and leads him to act really stouc and serious when in reality he's a pretty big goofball. He really likes eating basically anything that fits in his mouth just for the hell of it.
Also, he's about as straight as a circle.
There you go. Grey Agate.