Font Colour Changes from Photoshop to PDF

It could be a poscript issue or something mismatched with the font.

The easiest solution would be to duplicate the layer (hide the original for future edits) then merge the layer and save as a PDF.

Ignore my comment, it's not applicable...

That is really strange. It's like an odd clipping behavior is happening with the black fill. I think there could be some sort of glitch happening with that script typeface. Have you tested any other fonts to see if the same thing happens?

It might be more of a pain to do this, but I would consider creating this kind of a layout within either Illustrator or InDesign rather than Photoshop. The same background image can be used within a AI or INDD document. Illustrator and InDesign have far better type editing tools than Photoshop. You'll also have more options available when exporting to PDF. Plus, with Illustrator, if the fills were still glitching out in those script text objects those items could be converted to raw outlines. Then they could be joined using Pathfinder tools. That would likely yield a proper, more predictable fill result.