As a general rule we cannot recommend judging color correctness in the Mac Preview application or any of the Open Source PDF viewers.
Moreover, although PDF has become an ISO standard, Adobe invented PostScript and PDF, which is based on PostScript, and it has a commercial incentive to promote PDF, as well as standard compliance on all platforms.
Hints for Scribus users:
We highly recommend upgrading to the latest Adobe Reader version. Simply put, there is nothing else more capable of rendering PDF correctly. Whatever your objections were to older versions (and there were some substantial ones, most notably on Linux), the later versions, especially after 7.0.9, ameliorate the vast majority of them. And while it's often being discarded as being a "resource hog", it is still far more stable, bug-free and loads quicker than older versions. On Linux it now has a modern look and feel. Versions after 7.0.9 also have direct support for CUPS and offer many extra options for printing. Any PDF rendering issues with Scribus exported PDF in other viewers should be cross-checked with Reader 7 or higher before reporting bugs to us.
One of the major advantages of the latest Adobe Reader releases is the ability to "flatten" transparency in PDF 1.4+ files. This feature is important, because some printers still can't handle PDFs with transparency. Also, the PDF/X-3 standard, required by many printers these days, doesn't support transparency. While the PDF-to-PDF flattening remains a feature of Adobe's Acrobat program, Adobe Reader allows for creating a "flattened" PostScript file via the print dialog. The resulting PDF file can then be converted back to a PDF file with GSview or a command line tool.
We are aware of color mismatches when viewing PDFs which have some kinds of transparency in PDF 1.4+ files. This has been reported as a bug to Adobe.
A note to OS/2 and eComStation users
Unfortunately, Adobe doesn't provide new versions of AR for OS/2 anymore. The latest version that reportedly works on these platforms is 5.1, and it requires an additional runtime environment. The runtime environment can be downloaded here. The AR installer is available "> here.