WARNING: If you haven't found the mural and don't wanna be spoiled, click off now.



So there's been some confusion about the mural and the story it tells.

The story is that the lava and water queens were lovers, until the lava queen betrayed the water queen's trust. This resulted in war breaking out between the water and lava people. The lava people would get more radical, though not all of them did. The water queen remarried to a close friend and had kids with him, while the lava queen was betrayed and killed by her own people. As seen by the purple crystal in the water temple, as well as the blue and orange lighting throughout the temple, the water queen would come to forgive the lava queen.