Photoshop Elements :: White Background Appears Grey?

Still trying to learn my D7000
 
Yesterday, I took a number of experimental shots (a red phone cord lying on a white background). The white background (an artists white canvas lying on the floor) was well lit from above using 5600K lights.
 
The shots were all taken using auto focus, auto exposure, etc and in the view finder everything appeared to be correct, but on later viewing the photos, the white background appears to be grey.
 
I have attached a sample image to show the grey colour.
 
especially when using the auto mode when taking the photos.
 
I am not concerned about the picture quality only the grey background and I did not undertake a WB as I thought that this was part of the auto mode when taking the photo. the shot was taken by half pressing the shutter release butto to ensure that everything was OK then continuing to fully press the button.