Illustrator CS6 pdf question

[Sbrem]

For the Illy CS6 users; when I save a file as a pdf, with the exact same pdf options and settings as I used in CS5, the colors display incorrectly. So I created a test image, a 3 color, black and yellow on a medium gray background, and saved it as a .pdf with the default settings (as I have forever). When I look at it in the finder, it previews with the yellow as black; the black and gray are fine. If I open it with Preview, the Mac pdf viewer, it displays incorrectly as well, with the yellow showing as black. If I open it with Adobe Reader, it displays correctly. So why is this a problem? When I attach it to an email, it displays incorrectly and the customer calls and says "What the heck?" Then I have to say, "open it with Reader", but I'd rather it displayed correctly in the email. Any thoughts? And of course, thanks in advance.

Steve

and, this behavior is erratic...

[Command-Z]

Might be a problem with one of the color swatches. Are you using PMS spots? Change it to a process color and see what happens.

[GaryG]

For email proofing, we've always just exported as .png or .jpg (has to be rgb) at 72 or 150dpi
unless your client has to edit as vector.
They always just pop right up on screen in their email.
It doesn't matter what program they have or don't have.