Secret Santa 2024
The picture doesn't show for me only thing I can think of is shaders. You can check to see if your PC can run shaders by going to options and clicking the shaders box.
<Fish> How is being a dumbass a form of venting? Is this some sort of flatulence related joke?
If shaders is what you are talking about then solution is above me. But if The game menu is what you are talking about you have to buy a GUI texture.
The 'background' is called world shaders.

You can look in your data/shaders folder in your toribash directory for shader names.

Then, ingame, type /lws 'shadername'.inc. It only works when you have shaders enabled. For example, /lws meatwad_silver.inc will set the world shader for meatwad_silver in the data/shaders folder.

/lws stands for /loadworldshader