Last reviewed by Robert Prime — May 2026
Quick Answer: KDP requires print PDFs in CMYK colour space, not RGB. Convert your file: in Acrobat → Print Production → Convert Colors → Profile: CMYK → OK. In InDesign, set Document Setup to CMYK before exporting.
Full reasoning, why-it-happens, and the exact fix below.
UK note: UK-specific considerations apply — ISBN purchases go through Nielsen (not Bowker), VAT rules differ from the US (print books are zero-rated; ebooks carry 20% VAT), and GDPR applies to any email/customer data. See our UK self-publishing guides for specifics.
We see this come through our formatting queue at publishing.co.uk regularly, so the patterns and fixes here are based on what actually works at upload.
What this error means
KDP prints in CMYK — Cyan, Magenta, Yellow, Black — the four-colour process used by every commercial press. Your screen displays in RGB. When the two spaces collide in a single PDF, KDP's checker flags it because the colour conversion at print time becomes unpredictable: vibrant RGB blues can shift dramatically when forced to CMYK.
Officially, KDP "recommends" CMYK but accepts RGB. In practice, mixed colour spaces in one file (some images RGB, some CMYK, some greyscale) trigger a rejection more often than uniform RGB. The error reads "Your manuscript contains images in multiple colour spaces."
The rule applies only to print (paperback and hardcover). Kindle ebooks require sRGB and auto-convert CMYK input — opposite rule.
📎 Source: KDP's authoritative documentation on this rule is at KDP's print PDF colour-space requirements.
Why it happens
Mixing assets from different sources. Stock photos from Adobe Stock often come as CMYK TIFFs. Screenshots from your computer are RGB. Logos exported from Illustrator may be CMYK or RGB depending on document setup. Drop them all into Word and you have three colour spaces in one file.
Word and Google Docs are RGB-only. They can't even open CMYK images correctly. Authors export to PDF and assume the print partner will handle it. Sometimes KDP does, sometimes it doesn't.
InDesign with profile mismatch. Documents set up with "Print" intent default to CMYK, but if you place an RGB image without converting, InDesign keeps it RGB on export unless you explicitly enable "Convert to destination" in the PDF export settings.
Canva Pro exports "PDF Print" in CMYK by default, but only converts vector elements. Raster images you've imported stay in their original colour space.
Vellum and Atticus are ebook-first, RGB-only. Their print PDF export keeps images as RGB. For colour-heavy interiors, neither is the right tool.
The fix
Step 1: Audit your colour spaces. Open the PDF in Acrobat Pro → Print Production → Output Preview. The Separations panel shows which inks are used. If you see RGB inks listed alongside CMYK plates, you have a mix.
Step 2: Decide your target. CMYK is recommended for print. Convert everything to CMYK if your book is image-heavy. Convert everything to sRGB if you're going to dual-publish (paperback + Kindle) and want one image set.
Step 3: Convert each image (Photoshop):
- Open the image
- Edit → Convert to Profile → Destination Space → CMYK → Profile "U.S. Web Coated (SWOP) v2" (the closest profile KDP's print partner uses)
- Save As → TIFF with LZW compression (preserves quality) or high-quality JPEG
Step 4 (Affinity Photo): Document → Convert Format → CMYK. Same target profile. Export as TIFF.
Step 5: Re-place every converted image into your manuscript. Don't just convert the PDF after export — re-place in the source so it's clean.
Step 6 (InDesign workflow): Edit → Convert to Profile or use Window → Output → Preflight to find RGB images. Right-click each → Convert → CMYK. Export PDF/X-1a:2001 with "Output → Destination → Document CMYK" enabled.
Step 7 (Acrobat-only emergency fix): Print Production → Convert Colors → Convert all colours to CMYK → OK. This converts the PDF in place but quality is lower than re-converting source images. Last resort only.
Step 8: Verify. Re-open the exported PDF and check Output Preview's separations panel. Only Cyan/Magenta/Yellow/Black should appear — no RGB inks.
How to pre-flight it
Our free KDP Readiness Score reads every embedded image and reports its colour space (RGB, CMYK, Greyscale, Indexed). Mixed-space files are flagged red with image-level detail. We also catch the 30+ other KDP rules in a single pass.
Related errors
- KDP error: low-resolution interior images
- KDP error: transparency not flattened
- KDP error: embedded images too large
FAQ
Does pure black-and-white text need CMYK? No — text uses 100% K (black) only. The CMYK conversion rule applies to images.
Will my CMYK images look the same on Kindle? No — Kindle is sRGB. CMYK images get auto-converted but colours may shift. For dual paperback/Kindle, keep an sRGB master and a CMYK master.
Why does KDP say "recommends" CMYK if they reject mixed spaces? "Recommends" applies to pure RGB files (often accepted). Mixed colour spaces in one file is what triggers the hard reject.
What CMYK profile should I use? "U.S. Web Coated (SWOP) v2" matches KDP's print partner most closely. UK printers also accept "Coated FOGRA39" but SWOP is safer for KDP specifically.
Frequently asked questions
Why do I need CMYK if my book is black and white?
Even B&W PDFs technically have a colour space defined. KDP's print engine expects CMYK consistency. Convert and re-export to be safe.
How do I check my interior PDF's colour space?
Acrobat → Tools → Print Production → Output Preview. Toggle between RGB, CMYK and Grayscale. KDP requires interior PDFs in CMYK (for colour interiors) or Grayscale (for B&W). RGB interior PDFs are sometimes accepted but produce inconsistent print colour.
Will publishing.co.uk convert my RGB file to CMYK without colour shift?
Yes — we use ICC profiles tuned for KDP's printing process (typically GRACoL 2013 CMYK for colour, sRGB-to-Grayscale for B&W). The conversion preserves perceptual colour as closely as the gamut allows. We preview every conversion before delivery.
Why does the cover use RGB while the interior must be CMYK?
KDP's cover printer uses RGB workflow internally and converts to CMYK on press. The interior printer uses CMYK directly. Matching each file to its target press is what eliminates colour-shift surprises in print.
Related KDP error fixes
If you got the rejection above, you may also want to check these related issues — they tend to cluster:
Full list: KDP formatting errors hub · KDP rejection fixes hub · KDP rejected my book
About this guide
This page is part of a series of UK-focused KDP rejection guides at publishing.co.uk, each documenting a specific reason KDP can reject a print or Kindle file and the exact fix. Written by Robert Prime — founder of publishing.co.uk, co-runs the LoveReading network, and has overseen 500+ KDP submissions through formatting work in this category (print pdf).
If you'd rather have someone else handle this and the other 35 issues KDP checks for, our formatting service is from £69 with a 3-day turnaround and a 100% KDP-acceptance guarantee.
Run a free KDP Readiness Score on your file before you upload — catches this issue and 35 others, in 60 seconds.
External references
- Amazon KDP Help — official KDP documentation
- Author Earnings reports (ALCS) — UK author income surveys
