First, welcome to the forum.
And now, regarding your question, as to how to get rid of the grey screen. Is the iPad screen overlayed by a grey shadow, are all apps grey? Or where you referring to the grey water background image?
If the latter is the case, you can go to Settings->Brightness&Wallpaper->Click on the Wallpaper preview's->Select an image and choose 'Set as Home Screen', or 'Set as Lock Screen'.
Or you can browse images with the Photo app, and change the home screen background image from there. When browsing images in fullscreen mode, you can click on the rightpointing arrow and than on 'Use as Wallpaper'.
If however, the whole display is grey, no matter what app you are in, the display is probably faulty and should be replaced by Apple.