I did that speculative junk what I love to Steven Universe. Basically, gems look like semi-transparent hologram dolls with visible energy lines (sorta their nervous system?) and homeworld gems have almost robotic looking bodies designed for pure function and/or an alien aesthetic appeal. The Crystal Gems assumed humanoid forms a few hundred years ago so that they are less terrifying to humans. Steven has the glowy glowy nerves too, but his opaque meat body normally hides them.