The picture quality is negatively affected after updating this iPad Air 2 to 15.7.7.

If you see unexpected behaviour or performance issue subsequent to performing a system software update, try a forced-restart - as this will often clear an isolated software issue:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

If the screen colours still appear to be distorted or unnatural, you need to check some key Accessibility settings that are intended to compensate for specific colour-vision issues:

Settings > Accessibility > Display & Text Size

Ensure that all settings enclosed within the red box above are switched OFF/Disabled.

Otherwise, depending upon your installed version of iOS/iPadOS, you’ll need to look at your Dark Mode settings:

Settings > Display & Brightness > [Appearance]

If you continue to experience difficulties, you may need to seek assistance directly from from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad:

Genius Bar Reservation and Apple Support Options - Apple

Your iPad becoming hot suggests that something is amis.

If the problem persists after performing the restart, it may be necessary to reset your iPad settings. While this reset will not cause any loss of data, as a precaution, it is always wise to ensure that you have a current iCloud or iTunes backup before performing the reset:

How to back up your iPhone, iPad, and iPod touch - Apple Support

When you are happy to proceed, you can perform the reset from iPad settings:

Settings > General > Transfer or Reset iPad > Reset > Reset All Settings

If the problem still doesn’t clear, you would be best advised to seek assistance directly from Apple Support - or Genius Bar - as previously described.