"So I downloaded some random ones just to play around and view what it would look like. Can see significant color shifting, but it does not effect the darkness of the photo. I still see a well lit photo, until it's printed. My histogram looks good, with even a bulk of it to the right of middle."... Your image source profile will not affect the "darkness" of your image. There are several factors that will affect the quality of the end product: the printed piece. A few are press and paper. One factor that you really cannot control, besides lighting, lens, and F-stop is your camera's RGB capture. Some capture "RAW" images; some capture at a factory preset RGB. Some give you the ability to set a given RGB in the camera. We have no way of telling, but it appears your images are saved as sRGB images. I recommend you get Adobe's Print Publishing Guide. Unfortunately, it is a bit technical and filled with terminology. However, that terminology is explained in great detail in hopes that you will better understand the logistics of setting up and preparing files for printing. You will be able to understand how the image profiles fit into the entire process. What you are attempting with your request for book prints is pretty complex. So, it will ultimately come down to creating a color managed workflow from the ground up that starts with your camera's ability to capture and your ability to color correct the images using what is appropriate for achieving consistent, high quality "prints". I can tell you that I have a system that is solid as a rock. You have to take into account that your files will be put into an "Open Loop" workflow when you hand-off to a printer. Yes, they will have a print profile. Most will use a standard CMYK print profile. Something like "SWOP Coated v2" ( note "coated" per paper on press ). Printers typically color calibrate their RIP to conform to that profile. Their profile is usually not given out to the public, but instead is used in-house only. Almost all printers will recommend image files saved as "Adobe RGB", then converted to "SWOP...CMYK". There are exceptions, but typically that is what you can expect and base your file preparations on. Some exceptions might include different print processes and equipment. Some specific printers were or are made to print photographs. Some examples would be High Fidelity offset printers, HP, Epson, etc., wide gamut multi-color inkjet printers. Some of those may actually prefer ProPhoto RGB image profiles where the print driver / RIP can maximize color output ( saturation, gamut, etc. ). But, you are not dealing with those applications, but are buying printing from a print provider ( Alphagraphics, Sir Speedy, PIP, etc. ) which is most probably a 4-color process printer, who may even had used a color copier to print your files ( quantity: 100 ).
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