My iPad has no colour

Well that is great!

This means there is a sulotion for this

I think I know what setting you have turned on.

Try to go to settings->Accessibility->Display & Text Size and see if Colour Filters is on.

Good luck!

You can try a clean install of your device after a factory reset:

First make sure you have a backup

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

Then facory reset your device:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

And set it up without a backup. See if the issue persists.

If it still does not work it is a hardware issue and will need service:

Contact Apple for support and service - Apple Support

If that solved it there was a software issue. Try restoring the backup and see if it still works.

if that made the problem come back the backup is the problem

Good luck!