Exported PDF loses text color

I've twice exported Keynote presentations as PDFs (then uploaded to a file server and downloaded—to a PC and a Mac), only to find the text color (dark brown/reddish brown) is often rendered incorrectly when the PDF is opened on the other end, usually as a very light blue or gray-white. The original file and original PDF render fine on my computer, my iPad, iPhone, etc., but it's been very frustrating to have otherwise nice-looking presentations marred by semi-legible text.

Any ideas? Am I doing something wrong, or have I run across a bug?