The most fitting background I could find for my avatar is the [item2=Innocent Sovereign Golden Fragment], but even then I don't think it's the best.

My avatar is meant to be a royal guard for an evil emperor, so something that looks like a throne room or a castle corridor would be best, and preferably with red, white, and/or gold coloring.

Interior backgrounds are hard! The first things that came to mind were or

Sadly a lot of the castle-y type items I could find are either very blue very dark or just not in the right colors The only red/gold/white ones I could find were but they aren't quite the right look I don't think. You might want to consider layering something with something like one of these instead? Hopefully one of those is useful to you!