I had a nag screen from from my Spyder calibration utility when I logged in today to say it could not load my personal monitor colour profile. I found "Use my settings for this device" was deselected in Colour Management and the default monitor profile set. I selected "Use my settings for this device" and the correct monitor calibration profile and all is now fine.

I did update my AMD graphics driver to the latest version yesterday and wonder if this has reset the colour profile to default? However, I've updated the graphics driver many times before and the monitor colour profile was never changed.