Shifting screen colors as phone is used, clouds of various hues!

My iPhone fell to the floor. The screen is fine, everything works as it should.

Except...

When I first turn on the phone (or after it sets for a time), I pick it up and it looks as it should. After a short time, a "cloud" in the center of the screen.

A black background will have a yellow cloud in the middle, blues of Facebook will have a yellow/green hue. A white background will show a purple cloud in the middle.

It seems to change shape and vary as I use it. Sometimes small in the middle, but the more I use it, it will be the complete screen. Then sometimes it'll be ok and then not.

I opened it up and checked all the connections. Nothing remarkable.

Thank you in advance!

So1oM