Feb 16 2020 09:49 AM - edited Feb 16 2020 09:52 AM
Hello @Gold4trees,
Perhaps you changed the contrast theme of your desktop. In your start menu search bar, type in "contrast" and select the first option. Scroll down and change your desktop theme to one of your liking.
Or perhaps you mistakenly changed the color scheme in excel. Refer here:
https://superuser.com/questions/423090/is-there-something-like-a-dark-background-excel-theme