Hello MichelleCohen_288,
Welcome to Microsoft Community.
Because your description here is "For some reason", I am not clearing the details of what you did.
The first thing that comes to mind, though, is that it looks like you changed the color mode of your system to "dark."
In Windows 11, for example, on the desktop, right click the mouse in an empty space, and then click Personalization - Color - Select mode, please make sure that you select the "dark" option here, you can change it to "light", the folder background will be displayed in white.
In addition, please ask if you have manually added a theme to the system, or are using some theme software or desktop wallpaper programs, if so, please turn them off completely or uninstall them completely, and then select "light" in the color options to confirm that the problem still exists.
Best regards,
Mitchell - | Microsoft community support expert from MSFT