I could string myself up! I spent forever working on a material for my mug. All was going well, then for no apparent reason I changed the render settings from CPU to GPU and my machine crashed. Of course I was so caught up in following the tutorial that I hadn't saved and versions for ages and found myself a long way back in my journey. I opened up the latest Auto Save from the Temp directory and all seems pretty good apart from the fact that everything is purple. Help!!! 
