?Windows adding unwanted colour to graphics

I keep getting an unwanted background yellow-brown colour
to graphics, including Excel graphs, and B&W diagrams that
I have scanned. Because it happens in various programs, I
suspect that it's a Windows problem. (It happens in Word
and Excel, but also in PaintShopPro.) It's not just a
screen problem, as I have had some scanned B&W line
diagrams print with this colour too. Because I had a
similar (but not identical) background colour in my
Display Properties, I thought this might be being picked
up, but changing the Display colour to white makes no
difference to the problem. Very strange and very annoying!

Any ideas?

Dave.