Hello there bot-net,
Thanks for posting here on the Apple Support Communities! This is a place where other Apple users can submit questions or respond to others to help lend a hand. Let's take a closer look as we do our best to provide some additional insight.
To get started, can you describe exactly what you mean by a shadow? In the image you're showing us, the background is partially opaque so it's normal part of the background and apps to still show through.
Otherwise, does the same thing happen on any solid white or black screens at all or in other specific apps?
In the meantime, take a look at these resources to check for any settings that may be related to what you're seeing:
Adjust the brightness and color temperature on your iPhone, iPad, or iPod touch
Use Night Shift on your iPhone, iPad, and iPod touch
We hope this helps get you pointed in the right direction.
Take care.