Converting from Pages to PDF changes colors

Pages v7.2 as its predecessors, does not like transparency (your apparent gradient in the first screenshot), and will render it as 72 dpi in the PDF — regardless of how you create the PDF from Pages. Also, Pages forces the RGB color model in the document, and if you are not using Adobe RGB or sRGB for your display profile, the PDF colors will not be true to the original document. Just another reason we don't recommend Pages for serious DTP and Professional print work.

There is a dedicated Pages for Mac Support Community available to you.

If Word is using the same Apple PDF conversion libraries as Pages, and other Apple applications, then this would explain why PDF files exported from Word behave similarly. It is not out of the realm of possibilities that Apple has yet again, modified the PDFKit and Print Operation frameworks for Mojave, and may have introduced collateral PDF imaging issues.

Do you have Affinity Designer? It bundles its own PDF v1.7 library and does not use Apple's frameworks for PDF generation. If you have it, create the gradient as you depict in the Pages document, with vector text over it. Export as either .psd, .jpg, or .pdf and drop into Pages where your current gradient resides. Now, export the Pages document, and compare results.

Not really seeing a difference. Can you post a screen shot?

See if it does the same thing in a different user account. If it does, try when booted in Safe Mode.

Use safe mode to isolate issues with your Mac - Apple Support

How did you create the PDF from Pages? Using "Export…" or "Print…"? Your pics aren't even close.

Sorry. Then I'm clueless. It doesn't do that on any of my Macs running Mojave. Perhaps someone else will have an idea.

You're welcome. I meant to ask, does it do that with any image or just the gradient?