Apple Watch Series 8 watch face

I'm going to assume you're using Always on, with a face, which when your watch is on, it has a white background, but with Always On, when the watch is not active, the white background goes black. This would be completely normal and is a battery saving feature as to keep the face white all the time would eat up your battery pretty fast. You can choose a different color combination for just about all the watch faces.

Here is a link on how to customize watch faces on Apple Watch --> Customize the watch face - Apple Support

My Apple 8 watch started switching from the screen display coloring and look I chose to a solid green background with black displays on the same settings I had chosen. I lucked into fixing it by going into mywatch on my iPhone, choosing accessibility, and Display and Brightness. In there I went to Wake on Crown Rotation and switched it to on. Now it maintains the display coloring I chose when I move my wrist around. No idea why this works or what I did to change it, but for now I’m happy.