Definition
CMYK vs RGB
RGB is the additive colour of screens; CMYK is the subtractive ink model of printing. Covers are printed in CMYK, so bright screen colours reliably print duller than they look.
The gamuts do not match. Vivid oranges, deep blues and anything neon exist on a display and simply cannot be mixed from four inks, so the printer substitutes the nearest achievable colour — which is why a cover can arrive noticeably flatter than the file. Convert and inspect in CMYK before approving rather than after, and treat a rich black as a specific mix rather than pure K, which prints as a washed grey over large areas.
Related tools & guides
The press-ready file, made for you
Upload your Word manuscript: Ceeryo typesets it and gives you a CMYK PDF with black on the K plate, a PDF/X output intent, crop marks and 3 mm bleed — and the plain PDF for KDP from the same upload.