This is something I have been doing for a long time, and is a nice way to change up the look of Theater View.
I was never a big fan of the background for the main menu...Many of you may already know this, but to change it:
1. Go to Options:Theater View
2. click on ...Theme:{theme name} and select 'Create Zip file of current theme...'
3. open the zip file you just created, and in the root of the folder there will be some image files. Delete them all.
4. Now add in any background images you want. I usually just do 1 so it is consistent, but have added up to 3.
5. rename the zip file to whatever you want (this isn't necessary, but helpful)
6. go to Options:Theater View
7. click on ...Theme:{theme name} and select 'install theme from zip file...'
8. Find the updated zip file and select it...
9. Enjoy!
I know this is a small thing, but hopefully it will help someone! There may be an easier way to do this, but I like being able to import the newly created theme file on all my JRiver PC's.