Should I use RGB or CMYK for my KDP and IngramSpark book cover?

The short answer to “RGB or CMYK?” depends on your printer. But the real question—why your printed cover looks darker than your screen—has a universal cause.

The Printer-Specific Rule

Amazon KDP: Use RGB. KDP’s system is built to take sRGB files and handle the CMYK conversion internally. If you convert it yourself first, you’ll force the file through two color conversions (yours, then Amazon’s), which degrades quality. Always upload your paperback cover PDF and ebook JPEG in the sRGB color space.

IngramSpark: CMYK is Mandatory. All images in your IngramSpark cover file must be in CMYK. Their barcode also requires a specific pure black ink mix (0/0/0/100). The best practice is to convert your RGB master file to CMYK only as the very last step before exporting your final PDF.

Lulu: follows standard PDF workflows. When in doubt, use the precise template they generate for your book’s specifications.

The golden rule to navigate all this: Always design and save your master file in RGB. Only convert to a printer’s required color space during your final export. Never convert back and forth.

The Real Reason Prints Look Darker

Your screen creates color by emitting light; paper creates it by absorbing light with ink. The RGB spectrum includes vibrant, saturated colors—think electric blue or neon purple—that simply cannot be replicated by any combination of printing inks. When your file is converted for print, these unreachable colors are mapped to the closest printable alternative, which is invariably duller and darker. This isn’t a flaw in any one printer’s process; it’s a limitation of physics that affects every print job.

What this means for your book cover:

• High-Risk Colors: Deep saturated blues and purples, hot magentas, and bright gradients will lose the most vibrancy. Expect them to shift noticeably.
• The Darkness Multiplier: A moody, midnight-blue scene on screen can print as nearly solid black. If your design lives in the shadows (roughly the 10–25% brightness range), consider lightening it before you finalize the file.
• The Ultimate Test: Order a physical proof copy. No on-screen soft-proofing simulation can fully replicate how your specific artwork will look on paper.

A Note on “Muddy” Solid Colors

Large, flat areas of a single rich color (like a solid burgundy back cover) can sometimes print with a slightly uneven, blotchy appearance on print-on-demand digital presses. This is because POD uses toner or inkjet technology, not the offset lithography of large print runs. Using a textured background or a gentle color gradient can help hide this effect better than a perfectly uniform fill.

Quick Reference Chart

For the other half of cover preparation—getting the physical dimensions, bleed, and spine width correct—refer to the cover size requirements guide or use the automated calculator.

Sources

• KDP Community: print cover in RGB — KDP accepts RGB, converts internally
• IngramSpark: File Requirements for Print Books — CMYK requirement
• VeritasCanvas: RGB or CMYK for KDP covers — conversion behavior and gamut discussion