White image area isn't white...

I have a postcard file that a customer sent us as a .JPEG. The white part of the file has a faint screen of blue, maybe 2 or 3 percent, when it is printing on any of our Postscript 3 Xerox printers. Now for the strange part. When I print it to our imagesetter the background is perfectly white. I open the JPEG in Photoshop and according to it the background is pure white.

I have tried printing it out of Indesign and also out of Photoshop. In Indesign I drew a white box over part of the background and it came out as a white block on the Xerox printers. Finally I tried printing it to a non-Postscript inkjet printer and it too shows the faint blue screen.

I tried turning off all the color management in Indesign and the printer driver but that had no real effect. Any suggestions?

Stab in the dark but is there some strange color profile embedded in the image? If you force a conversion to cmyk or even round trim to rgb and back to cmyk does the white stay 0 0 0 0 when it's cmyk again?