This is an age old question that litters the internet. I've been working in design for coming on two decades, so am fairly up to speed with color profiling for devices, images and proofing. I've sent countless jobs to many printers and have been happy with color matching in the past.
My greatest weakness until now was using standard, uncalibrated Apple displays. I've recently fixed that issue and am using a fantastic Eizo monitor calibrated with an iDisplay Pro. Which leads me to this:
I'm aware that PDFs displayed on screen - with all the best calibration in the world - should not be held as an accurate example of print colours. PDF viewers are infamous for inaccuracies.
Using my calibrated monitor I've set my InDesign working RGB space to Adobe RGB (the monitor can display 10bit) and CMYK to U.S. Web Coated (SWOP) v2. My document is using the working space profiles.
I export the PDF as a PDF:x-1a, which has always been the safest bet for print houses in my experience. I don't need the extra features of later PDF versions and am happy with anything flattened and no transparency. It converts to my CMYK working profile.
The PDF looks very washed out in Preview.app (relative to the active document in InDesign) on my calibrated Eizo and calibrated Apple screen. I don't worry as this has always been my experience. It's a CMYK space being viewing on an RGB monitor and while it could do a lot better at emulating the colors, it's never going to get it perfect.
Just to be certain, having not used this calibrated screen before with InDesign for print output I try a similar experiment with JPEG. I export the page as a jpeg, specifying it uses the working space of Adobe RGB.
To my surprise, the JPEG looks equally washed out. I confirm it's using the embedded Adobe RGB profile and check it in PhotoShop, just incase Preview.app isn't showing it accurately (which it always does for jpegs).
Although my Eizo displays 10bit color and doesn't suffer from the issue of Adobe RGB documents not displaying accurately, I convert the InDesign document to sRGB just to rule out the issue. Exporting as JPEG, I confirm the document is to be converted into working sRGB.
Same as result 2. The jpeg is significantly washed out compared to the colors I was using in the active InDesign Document.
We're past the days of having to convert all images used in InDesign into CMYK before import. Its conversion engine is know to handle any exporting pretty well. If you can use Photoshop to convert an RGB profile into a CMYK profile, why would Adobe provide a poorer result automating this in InDesign? It's their same conversion engine.
Any images placed in my InDesign document look accurate to how they are outside of it, such as in Photoshop. It's the export that skews the colours.
Some people blame RGB > CMYK conversions. I've done plenty over the years and know there's a difference when flicking between the original and conversion but nothing as inaccurate as when viewing an exported rgb jpeg from an InDesign document.
As far as I know (and may be wrong on this). InDesign documents aren't strictly calibrated to CMYK or RGB until export. They are a collection of elements profiled to both spaces and it tries to display them as accurately as it can relevant to the working RGB space for monitor presentation. So using RGB space images in the document and exporting as an RGB jpeg shouldn't see massive color shifts anyway.
My system is set up for a full 10 bit color pipeline and macOS 10.13 as well as Adobe CC 2018 are 10-bit enabled. I tested everything above with my monitor set to sRGB and color spaces to sRGB too with the same results.
Although I'm stressing the calibration measures I've taken, it should only matter for print accuracy, not comparing a working document with an export as the final section of the color pipeline in the OS - altering for the monitor profile, would skew colors similarly on an uncalibrated monitor/profile (between the active document and the exported jpeg, as long as the software viewing both are color profile aware and perform conversions correctly).
Am I missing something? If my exported jpegs has colours so deviated from my working document, with everything calibrated and profiled, I don't feel I can send my PDFs to print with confidence. Although the project's concern is with PDF color accuracy, the question pertains moreso to JPEG exporting as, unlike PDFs, I trust the color accuracy on my monitor of any images converted through a color-profile-aware pipeline like this (RGB space images exported as an RGB space document with the entire pipeline color-managed).
I've noticed this question was closed due to requiring a 'specific setup, file, or interaction with you or your machine. Questions on this site should be potentially useful to future visitors'
I don't understand the lack of usefulness? Wide-gamut monitors are only going to exponentially increase in use and this is a very pertinent question to them. The lack of people using Adobe RGB as a workspace in InDesign and the relevance of doing so on a wide-gamut monitor is surely a very useful question to have as a resource? There is little to no information about this elsewhere, I googled it extensively before posting here (InDesign usage in regards to wide-gamut displays)
If the closure related to the niche use of a wide-gamut monitor, they already have strong adoption with graphic professionals and are only going to increase until their commonplace. I see no other specifics in my question that's intangible or irrelevant to others? The file being used was irrelevant and the model of my monitor is irrelevant.