Strange happenings with iPhone 8 (updated). Can you help?

About a week ago, the home screen turned black. The pages with the icons are white as they have always been. I checked 'settings' and it still indicated white. What would cause this change in background to black? It is difficult for me to see the initial pages w/icons because they all have black background but if I click on them, the pages are normal.

I called the local tech phone repair company but they are on vacation. Do you fine folks have any idea what has happened and how to fix it? I would be thankful and it would save me $$$ when I have the appointment on July 6th.

I cannot afford a new phone and I am on my "friends and family" plan and cannot change that. Thanks for any guidance.