Beware Overprinting White
Martin D. wrote to us last week with a fascinating problem he encountered with a client: White text over a black background was disappearing when printed. He noticed that it would also disappear when Overprint Preview was turned on. He had written this up on his blog (in German).
Selecting some of the text and taking a quick glance at the Attributes panel (Window > Attributes) shows that the text is set to Overprint. But because the text was set (by the paragraph style) to Paper color, the Overprint Fill feature is grayed out in the Attributes panel. That's right, it's on and grayed out.
Of course, it's easy to select all the text, change its fill color, turn off the Overprint Fill checkbox, then set the color back to Paper. But the real mystery is why (and how) the paragraph style was set this way. And the answer is: It's a subtle but dangerous bug.
You can easily create a paragraph style, set its color to Black (or any other color), and turn on the Overprint Fill checkbox in the Character Color pane of the paragraph styles dialog box. Now, if you later change the paragraph style so that it has a fill color of Paper instead, the Overprint checkbox turns off and grays itself out in the paragraph styles dialog box. That makes sense: After all, no one would want their Paper text to overprint (it would just disappear).
But a funny thing happens on the way to the finish line: After you click OK (to save the paragraph style), the text on the page does turn Paper... but the Overprint Fill is not turned off. The checkbox remains on (though grayed out). This appears to happen in both CS3 and CS4.
As the Sewer Urchin would say: "Not good. Very bad."
Even saving as INX or IDML doesn't fix the problem. The only good solution is to edit the paragraph style, change the color, turn off the Overprint Fill checkbox manually, then set the color back to Paper.
Fortunately, the Preflight panel in InDesign CS4 can find these errors easily. You have to make a custom preflight profile that checks for overprinting of white or [Paper]:
So: Eternal Vigilance! Preflighting! Spoon!