workspace background is red when image is loaded in PS

I don't know what I did to cause it but suddenly the workspace has become red when I load an image (See screenshot attached). I have tried changing in preferences but as soon as I load image this background re-appears. It happens with any file I load. I am on Windows 10 and PS CS4. Just before, I had started to use the ellipse tool. At some point I could pick a color and picked that red (for the ellipse)