Digital Devices use RGB – so your monitor, TV and cell phone all make up the millions of colors that you see using just three colors Red, Green and Blue.
However, the print process uses a different color gamut called CMYK (cyan (blue), magenta (a purpley-red), yellow and black) to make up the colors that will be in your book.
This means that, when you send me RGB files, I place them into InDesign and then allow the the PDF creation process to convert the colors over for print.
When this process is complete, you may see a color shift. In most cases, this will be minor, but can be particularly noticeable with blues and purples.
https://www.printingforless.com/color.html offers pictorial examples, as well as a great overview.
I do not do color corrections on supplied artwork. If the shift is great and you are not happy with the results, it’s best to have your artist work on the piece, and then run test prints to ensure it will be what you are looking for. It’s important to note though, that color will also vary slightly on every printing device so there may still be variations even after confirming color on test prints.
If you’d like an in-depth look at the differences: https://www.printingforless.com/color.html