The diamonds excrete life juice that makes gems function. Yellow’s juice makes them take form, blue’s juice makes them have emotions/sentience, and pinks juice keeps them emotionally composed. We have yet to see what white’s juice does (maybe it gives them power?)
When gems act out or aren’t working to the diamond’s standards, they have some of the life juice forcibly removed and they are made into decorations. However, they remove only 2-3 of the diamond’s juice.
The yellow wall gems had all but blue’s juice removed, cause they can still chat and feel embarrassed, but their bodies are flat due to not having yellow’s juice and they don’t talk to others due to not having pink’s juice.
Note how there are empty spaces on the other side, possibly reserved for more gems who act out.
The blue statuesque gems had all but yellow’s juice removed, since they have bodies and can blink, but they don’t emote or speak.
Side note: Look at how large they are compared to the others. Maybe these are older gems created when homeworld had more resources?
They keep these gems as decorations to threaten the other gems, keeping them from wanting to rebel out of fear. When harvested, they are kept alive as a punishment, but they are effectively disabled.
This also might be what happened to white/pink diamond’s pearl. She had all the juice removed except maybe white or yellows, so she is stuck, unable to move, speak (white diamond is speaking through her), or think. She is effectively a symbol to all other gems that acting out is not acceptable.
Bonus theory: Pink’s room has gems that can quickly build things for her, similar to rose’s room. Are there pebbles in rose’s room, or is the temple sentient? Does the crystal heart have something to do with that? Maybe the temple is sentient like the walls and statues of homeworld, but it only has pink’s juice. Because of that, it can’t form a body or think, but it can preform actions internally.
Or maybe, as evidenced in the episode “open book”, when the diamond’s removed pink pearl’s sentience, pink diamond held onto it and put it in the temple, so rose’s room contains pink pearl’s mind.
Go back and watch s1e46 “open book” while picturing connie as pink pearl and steven as pink diamond. It’ll blow your freaking mind.
One way or another... FAMILIAR WAS A GREAT EPISODE!! ✨💕👌👌👌