Illustrator Color change

Yeah the files are client created using Canva. So I'm sure there's some issue there itself. I don't really have this problem any other time. That I notice anyway. I'll have to jump into indesign. Thanks for the help!

Agree, the problem is that Illustrator isn't a PDF editor - it can just import (and sometimes mangle) other PDFs, and does a great job of re-opening its own PDFs.

Sounds like a job for InDesign. It can place PDFs, and keep the colours unchanged. You can add text etc. If you want to add more things like a fancy graphic title, make it in Illustrator with a transparenct background and place that. 

If you want to do more detailed editing get the designer's original file, and use the original app. The idea of freely editing in the app of your choice has trapped many people over the years, but it doesn't fly.

Illustrator is not a general purpose PDF editor.

These things happen when you open PDFs in Illustrator. A PDF can contain images in different color modes. An Illustrator file can't.

You might want to take a different approach to this project. You can extract the original files from the PDF using other techniques or have your clients hand ou the original files.