Will a white box in the lower layer cause overprinting issues?

Question

Adobe Illustrator CS6

After setting the document dimension and bleed, I realised that the default white artboard won't go into the bleed region (5mm), and that remains as grey. So, almost out of OCD, I made a pure white shape stretching towards all the bleed borders and set it in it's own locked layer, like a white base, for all of my 200 artworks in a particular project.

I didn't think that this would be an issue since it's white. All the artwork were placed in their own layer above this "base layer".

However, I came across some shapes which were red (0,100,100,0) CMYK. They looked fine until I applied a 75% opacity. So, they look reddish when overprint preview is OFF/ON, and pinkish if overprint preview is OFF without a white base.

Why is this?

Am I missing something funadamental about print. Should I leave the white base layer in my 200+ images or go through all of them deleting the white base? They will all be linked into InDesign for a book design.

Answer 1

Illustrator has a funny way of always overprinting white. According to the developers this is necessary in order to ensure gradients and other objects containing white separate properly. Things have improved the last couple versions where this is concerned, but CS6 was still a version with some unexpected white overprinting issues.

To be honest, I don't fully understand your need for the white box. I mean, the grey area outside the artboard would simply be your bleed and should not be seen as critical in terms of exact color. If the color is correct on the artboard, then the bleed color will be the same.

You are seeing a difference because of the grey pasteboard/clipboard outside the artboard. As it's part of the bleed, and not part of the artwork, the grey pasteboard isn't going to print. Overprint preview is giving you an accurate representation of colors (assuming good calibration). With overprint preview off Illustrator isn't simulating ink so colors may shift a bit.

Essentially, if colors are correct with overprint preview on then you should be fine.

I can't replicate your issue here. I'm not seeing any difference in a 75% 0/100/100/0 rectangle over a white base or without a white base. However, my pasteboard grey may not be the same grey you are using.

If it were me, I'd not add random objects (white box) just to change how things look on screen. If the object isn't needed for reproduction, then the object shouldn't be needed.

If the grey bothers you that much, simply create your artboard at bleed size and don't use the bleed settings in the document setup.