Only a slight move is needed to give your image some color. 4. Convert to CMYK. Blurb’s plug-in for Adobe InDesign and Blurb’s PDF Uploader work best with CMYK images. If your images are already in CMYK and you're done editing them, you're all set. Put your CMYK images directly into InDesign or whatever program you'll use to create your PDF.
codemankino: And that would give you exactly the same result as if you converted the layered file from RGB to CMYK in the first place.
I still do not understand what you mean by "white transparent bar." If something is 100% transparent, it has no color at all. It is not white or any other color. Also, in the CMYK printing process, there is no way to 'print' white because there are only four ink colors & no combination of them will produce white. xQhW0.