We are trying to export a PDF from browser files with a semi-transparent rgb color over a background image to PDF/x-1a in order to change the color space to CMYK to send to a print vendor. However, when we output, it removes the transparency and makes a solid color, which covers the image.

We've tried using @page { prince-pdf-page-colorspace: cmyk } and using an ICC profile in the output intent, but it isn't fixing the issue. Does prince support an export with a semi-transparent color over an image and I'm just missing something?

Thanks for your help.

PDF/X-1a does not support transparency, so if you check the Prince error log you should see something like this:

error: stripped transparency from page to comply with PDF/X-1a:2003

Can you use PDF/X-4 instead?