While printing a document, the image color is getting changed from gray to black.

@rob day, thank you for your effort and your detailed explanations. You are probably the most informed and most helpful member of this community.

But before I mark your answers as correct, please allow me to make a conclusion (not a very optimistic one, I'm afraid).

You said that the softproof might be misleading and unreliable and that's very serious and it can ruin months or even years of hard work.

I even checked the PDF at the printery, on their monitor, but even that didn't help me. So something is very rotten in all this. This misled me and ruined my hard work.

In the past I had to deal with some cheap unprofiled printeries, which was a real nightmare, but ironically, now I understand that some of them were not that bad. Now I regret choosing this super-duper printery. I got no benefit from it at all.

Also, I saw no benefit from converting my images to that "Black Ink" thing. Everytime I learn something new on this forum, I apply it to my work in order to improve it, but in the end, I gained nothing from that.

This printing process is not so orderly and full auto as I expected. I thought that it is sufficient to prepare the document in accordance with a certain standard, so the printer can accurately reproduce it. But there're other variables in the process, and also, the human factor is not fully excluded from it.

The test-sheet that I got recently was bad. The blacks were too intense, everything was too contrasty, some details were lost, you can print that at home. I was given like 5 minutes to visualy evaluate it and to sign it. I wish I could do something at this point, but I don't have the necesary knowledge.

I asked the tech guys to help me, I showed them prints from other places as an example of what I want to achieve, but it was futile. As I said before, the communication with them is not that good.

I also don't know whether there're some losses or other problems during the CTP (computer to plate) transfer. And I don't know how much the human factor plays a role in that. Maybe they messed up something at that point.

So, as I said: always ask for a test-print before making any payments or agreements. If the printer refuses that, if they charge too much for it or if they try to lure you with promises  - just run away. It's not worth it.

Cause, in the end of the day, if something goes wrong, no one will blame the printer and everyone will blame you.

@Eugene Tysonand @Jumpenjax, thank you for your replies.

I do communicate with the printer, but the communication is not so good.

The 1st thing that I asked them for (before making any agreements) was a test-sheet, but they demanded too much money for it. But maybe this was a misunderstanding. The salesperson seemed to confuse that with a test-print of a complete book. That's how bad the communication was. Sometimes you have to speak to people who have never worked on a press (they are the ones who answer the calls).

The communication improved after I met their tech people. They were kind and helpful and they assured me that everything will be OK. They also promised free test-prints if I become their client. But after I gave them an advance payment, the communication gradually worsened. Now I can't leave the money behind. Huge mistake.

Now whenever I (politely) complain about something, they say: this is how things are done; you need a $20,000 calibrated monitor to judge that; we can't change our modus operandi especially for you; it's too late - the stuff is sent to the press; and so forth. They even use exclamation marks in their emails as if they're blaming me or something.

The only thing I was allowed to choose was whether the print will be darker or brighter. I guess that this has something to do with the ink density. I choosed brighter. But when I went to see the test-sheet, it was quite black. Everything is wrong, but they are assuring me that this is it, this is how it should be. That's why I didn't know how to react. Also I expected that everything will go smooth and automatic, without the need for any interventions. I'm very confused.

I also showed them some old prints that I got in a cheap non-profiled printery, which (in some ways) looks better than their prints, but they dismissed that.

They also refused to print the book cover and the color tipped-in page that I asked for on offset. They said that this is a low-volume job and that digital is a better and cheaper solution, so I accepted, but the price I got was still high. I guess that they do this to save money or other resources for themselves. You are constantly reminded that your order is small, which means that you can't complain much.

Something is wrong here, but I'm not an expert, so for now I avoid arguments. What you need in such situation is a 3rd party - a competent and impartial observer or a judge (sort to speak).

Always make test-prints before you make any agreements or payments.

You're better off showing the printer what you are expecting compared to the results you were shown. 

Explain your concerns to them - they can help you out much better. 

There's a lot of variables at play.

@rob day hit the nail on the head with the Display Rich Blacks and Output Rich Blacks setting you mentioned. 

100% of the time it's best to communicate directly with the printer regarding output expectations.

If it is a true printer ask what the dot gain on the press is, if it is 20 percent or higher, that would cause the black to plug up the dark shadows. I would ask the printer. You can lower the dot gain on your side too. 
https://screenprintingmag.com/predicting-and-managing-dot-gain/

Can you share the top profiled grayscale you placed in InDesign?

Hi @sd5e8a , Is the printer saying the proof is a contract proof—a proof they can match on press? Unless they are actually running a press proof, or they have capability of outputting a contract digital proof that imatates the press conditions, I doubt you can trust the proof.

Keep in mind offset profiles are not exact—the actual profile of the press would change depending on the black ink density they are running.

If you are using an uncoated press profile, I assume you are printing on an uncoated sheet? Did the printer recommend the PSO Uncoated v3 profile? Is the digital proof on an uncoated sheet which is similar to the sheet you will be running on?

Can the printer show you samples of 1 color grayscales printed from their press on an uncoated sheet? That might tell you how 100% gray is actually going to print. An untrimmed press sheet would have color bars with 100% black.

The Appearance of Black Print/Export Preference only comes into play when you export or print to an RGB destination—with Output All Blacks set as Rich Blacks 0|0|0|100 CMYK converts to the RGB Destination as 0|0|0 RGB (absolute black).

They "showed" you the print or mailed you a printed sample? Unless you're looking at the actual printed sample there are too many variables to go into. If you're looking at the printed sample and it's that darker/muddied, it looks plugged. Too high a line screen for the quality of the images. Often what I was viewing on my calibrated monitor was different from the proofs I received. Every vendor was different, so I would either have the vendor adjust the files to get to where I wanted, or I would make a 2nd set of my images for that specific vendor and adjust them until they printed how I wanted.