Hi annfromweymouth,
Thanks for contributing to the Apple Support Communities.
If you are seeing inverted colors on your iPad, the first thing to check would be the Accessibility settings, as outlined in the User Guide:
Invert the screen colors. Go to Settings > General > Accessibility > Display Accommodations > Invert Colors, then choose Smart Invert or Classic Invert. Or use accessibility shortcuts. Smart Invert Colors reverses the colors of the display, except for images, media, and some apps that use dark color styles.
Display accommodations - iPad User Guide
If it is not due to an Accessibility setting, based on the series of events you described, with the iPad falling on the floor and then having display issues, the best course of action would be to have the device serviced:
iPad Service Answer Center - Apple Support
Choose the service and repair option that’s best for you.
Send it in: Request a box and send your iPad to an Apple Repair Center.
Bring it in: Set up an appointment at an Apple Store or an Apple Authorized Service Provider.
Contact Apple Support
If you wanted to be sure it's a hardware issue before seeking service, you could also restore the iPad to factory condition. This Support article has information on how to back up your iPad and then restore it as a new device:
Restore your iPhone, iPad, or iPod to factory settings - Apple Support
If you see the same issues with the display after the iPad has been restored, then it needs to be serviced.
Sincerely.