Error "...document contains both CMYK and RGB color modes"

When I save the PDF and open it in Illustrator, I receive the following error:

“This document contains objects using both CMYK and RGB color modes. Illustrator allows only one color mode per document. Which color mod would you like to choose?”

Why does fmt=pdf,rgb produce CMYK objects when the file in Illustrator?

Solution

If the original Illustrator file was authored in CMYK, then all the artwork is set to use CMYK color values. Even when you use fmt=pdf,rgb, Scene7 still renders text and vector artwork using the color mode it was authored in. So, any CMYK images are converted to RGB.

Most printers prefer that PDFs are rendered as CMYK (fmt=pdf,cmyk)