Opinions and Suggestions, Please

My new betta tank has a black backing which makes it hard d to see my black betta. It won’t do any good to scrape the black off be case the filter box is black too. Could aI do anything to the inside of tank? Or, should I move my white betta to the new tank and the black betta to the other tank. White betta’s tank is 10G. Do you think it will stress her to move her to a 5G? Suggestions?Last pic is the 10G with a black trash bag in back which I could remove.

I dont know how much it would stress her but I think a white betta would look stunning against a black background

I really don't think it would stress her out very much at all. It endured a lot more stress while being shipped to you. When you move them, have the tank lights out and keep them out for several hours.

I agree, white on a black background would look great and moving them should not be bad but follow @Fishmanic advice it will help settle them down with the lights off.

When you do turn the lights back on, put on room lights first about an hour before turning on the tank lights.