Some PDF readers offer settings for custom text and background colours in documents (I know PDF-XChange does, it’s what I have on my work computer), but this of course doesn’t change image colours and can be glitchy if there’s for example text as an image.

If you already have the PDF as separate images, IrfanView has a nice batch mode that you can use to perform the same action to an entire directory’s images, so you could invert all the pages with a couple of clicks. GIMP probably has something similar, but it might be command-line only.