Connie while talking about Lisa who I said represents Rose said this in Open book. "Unlike Art the real World cannot win against the iron chains of authority."

Dogcopter who I said represented Bismuth says this. "Art is all about Communication. Art is a conversation. Make sure you make a statement with it."

If you put them together it makes this.

Unlike Fusion, the Real World( I looked up the definition of Real world and it says our lives individually. So this means us standing alone.) cannot win against the iron (metal) authority.

This means a fusion was used to beat the metals in a war. I believe the gem in the mural, formerly believed as Rose, was actually a fusion of all the diamonds. The moon goddess. There are 14 figures that are shown around the fusion and there are 11 colors of diamonds. Ruby, Sapphire, and Emeralds are considered precious. They can even cost more than diamonds depending on the quality. This would give you 14 exactly. The fusion has a diamond in front of her and the moon goddess has a diamond in front of her. The star on her chest is Rose's contribution to the fusion. Like Rainbow Quartz's leg warmers coming from Pearl.

I believe that homeworld is okay with fusion to defeat an enemy but not for love.

Also the metals's outfits in the mural have a upside down triangle. Pearl's original design(even though it's not completely cannon there is a reason they made it that way.) had a right side up triangle. I believe that before the war the upside down triangle was for metals and the right side up one was for gems. After the war that the gems won they were overjoyed because of the diamonds winning the war. So they adopted the diamond as their symbol and connected the triangles.

Lapis is the truth stone and also the stone of obligation. She has both a right side up triangle and an upside down triangle. This to the gems was like a diamond so they didn't see her as a threat, but the split showed that she had loyalty to the metals. She was a spy for the metals towards homeworld. They found out that she was a "backstabber" so they did it to her. Thus trapping her in the mirror. A partial part of the spy part came @TrevorFord but I added my own thoughts to it.