I hope this theory hasn't been posted before, but here's what I see on the mural of the four diamonds. Here's a picture so you can see what I'm talking about. All credit goes to its rightful owner!!

I believe they are holding the planets their moons they've colonized. '

White Diamond, in her hands, is holding Homeworld. This makes sense since it's speculated (confirmed? I think only speculated) that WD has the highest authority of all Diamonds. Around her are other important/near planets Homeworld has colonized. The one's with a line across might be planets with rings around them. The small orbs are their respective moons. They might add the moons to the murals due to the fact that maybe all moons are used with the same purpose as the Earth's moon.

Then there's Blue Diamond; I don't see anything too important about her mural. Just more planets. The only interesting characteristic to point out is that she has no moons. This might be because the planets she has colonized aren't for harvesting, fighting or anything similar, just to live on and plan stuff out? Since it's speculated she's like the thinker or philosopher of the diamonds. idk. I'd like to see your thoughts on hers, I don't really have a strong opinion about hers.

Now Yellow Diamond's interesting. Over her head there're planets, nothing too weird, but what captured my attention were the orbs on her hands. I first thought it could be the corruption weapon, because of the whole "light" thing. I also think they might be very important planets, which ones? No idea, but I believe they can be planets due to the moon of each "star orb". Surely, if it was the weapon or something other than planets they'd make it symmetrical, as the rest of the mural.

Finally there's Pink Diamond. PD is holding only one planet, with one moon. I highly believe that it is meant to represent Earth. It was her first (and last) colony, or maybe her most important colony. This also makes me think that PD is the youngest/newest diamond and the other diamonds might see her as the "little sister" or "rookie".

Those are pretty much my thoughts, they're not very groundbreaking and probably not too original but I hope I made someone realize something new today. Please tell me what you think about this! Thanks for reading!