I generated a PDF file from Pages, and now I want to know if the images are RGB or CMYK. What do I do?

The only answer I have is expensive: get Adobe Acrobat Pro.

* Open the PDF in Adobe Acrobat Pro.
* Go to Advanced > Preflight.
* Highlight any profile, for example "List all images".
* Execute.

In the resulting window, expand the data for all image and check if it is CMYK or RGB.