When placing an image within Indesign, a ‘trick’ (often lazy designers use) may cause variations of colour which may seem to be the same colour visually on screen. If an image does not cover a intended area on the page, you cannot simply add or colour pick and fill the background of the picture box.
A simple way to check to make sure this will print correctly is to view your separations. Turn the applicable plate off and you will visually see the difference in the cmyk breakdown of the intended colour.
In order to fix the problem, the original image must be extended in Photoshop. To correct, use the colour picker to select the colour you wish to extend, then resize the canvas appropriately, using the background / foreground colour as the extended area.
Replace the image in Indesign, remove any background colour applied to the picture box.
Finally, check your separations and you should now see no difference within the breakdown once the separation is turned off.
