I am using Illustrator CS5 and the grey background around the outside of my canvas/page I used to have and loved has gone white. I do not know why. I can not change the colour in preferences-user interface, as this was introduced in CS6. I have tried ticking and unticking the overprint preview and this makes no difference. Any help would be much appreciated. Thank you.
I bet "Hide artboards" was accidentally clicked or keyboard shortcutted. Go to
View > Show Artboards (... if I'm correct. Otherwise, it will still say "Hide Artboards"). Let me know if this helps.
View > Overprint Preview
Turn that off if you want to see the tinted pasteboard around artboards.
It could also be
Hide Artboards as @TimesWasting suggests
This could be it. Pull up the Artboard Options dialog box from the flyout menu of the Artboards panel. Under "Global", is the box checked that says "Fade region outside Artboard"? If so, uncheck it and it should go back to gray.