Same propblem here. I read threads of color maps and RGB and calibration... It's the same friggin Keynote file with a few slides duplicated/edited. The duplicate/edited slides export with dull, ugly colors. Preview looks fine, but I display PDFs with Adobe reader on other computers. Can this be fixed?
Alright, this is what has worked for me.
First to answer the question whether to use "Export to pdf" or "Print->PDF->Save as PDF" or "Save as PostScript" – I prefer the "Export" option for one reason: this method is the most accurate when it comes to object coordinates (images, lines, etc) AND custom slide sizes, while saving as PostScript is very cumbersome, especially when it comes to very custom, pixel-based slide sizes.
1. I have first exported the keynote presentation to pdf
2. opened it with Adobe Acrobat X (to witness false colors)
3. Now go to "Tools->Print Production->Convert Colors"
4. Ignore options, until the one which says "Output Intent" with a checkbox "Convert Colors to Output Intent". Select the profile "sRGB IEC61966-2.1"
5. Push OK.
Hope it helps.