Grey or washed out images displaying in Illustrator.

Appreciate the confirmation, I was sort of suspecting it may be a GPU issue (which is sort of over my head). However, I've tried saving it on 3 different computers, all three of which are less than 2 year old Macs (one is brand new), and got the same results when Saving As PDF.

What kind of PDF are you exporting?

Originally I was saving as the default "Save As" PDF, but I tried every possible variation, including changing color profiles. Doesn't seem to be a color profile issue, I even went as far as inserting different PS saved files—JPGs, PSDs, TIFs, came out the same every time. Compounding the confusion is that there's no rhyme or reason to the discoloration, sometimes other photos will suddenly change colors if I import other image files. Files that worked perfectly fine for the last weeks are also subject to the color change. The most success I've had in reverting the colors is by dropping TIFs or PSDs onto the artboard, for some reason that reverts some of the images back to normal, but it also changes others in the process.

How do you export or do you save as PDF?

Save as

What is the output profile?

The whole book, along with all the images are RGB as the book being created will be primarily distributed online. Should be straight forward. Initially I assumed I may have been accidentally importing CMYK files, or that my file was CMYK, but I meticulously looked at every photo repeatedly. The only thing I could think is that some of the vector objects are grayscale, since it's easier to adjust greyscale colors rather than with the RGB slider bars. I've done it many times before, obviously greyscale doesn't conflict with CMYK or RGB when exporting, although perhaps it does with the last update?