If you’ve ever submitted a book cover and had it come back with washed-out colours, or wondered why your designer keeps asking whether you’re publishing to print or digital, the answer usually comes down to two letters: RGB or CMYK. These are the two colour modes used in publishing, and choosing the wrong one for a given platform can mean your cover looks nothing like you intended. Here is what each mode actually is, and which platforms require which.
What RGB and CMYK Actually Mean
RGB stands for Red, Green, Blue. It is an additive colour model, meaning colours are created by combining light — the more light you add, the closer you get to white. RGB is the native colour space of screens: your monitor, your phone, your e-reader. Because it works with emitted light, RGB can reproduce a very wide range of vivid, saturated colours, particularly bright blues, purples, and greens that simply cannot be reproduced in print.
CMYK stands for Cyan, Magenta, Yellow, and Key (black). It is a subtractive colour model used in physical printing, where ink is applied to paper and absorbs certain wavelengths of light. The more ink you layer, the darker the result. Because it depends on physical ink rather than light, the CMYK gamut — the range of colours it can reproduce — is considerably narrower than RGB. Colours that look vibrant on screen will often appear more muted when printed in CMYK.
Platform Requirements for Print Books
The print platform you use determines your colour mode requirement, and these requirements differ significantly between the two major services.
Amazon KDP Print accepts and prefers RGB files. KDP handles the conversion to CMYK internally as part of its print process. This conversion is generally reliable, but it is not perfect — particularly for highly saturated colours. KDP strongly recommends ordering a physical proof copy before approving your book for distribution, precisely because colour shifts can occur in the conversion. You cannot fully evaluate print colour accuracy from a digital preview.
IngramSpark takes the opposite approach: it requires CMYK files for print covers and interiors, and authors must perform the conversion before uploading. IngramSpark’s file creation guide specifies a maximum total ink density of 240% — a technical limit that prevents colours from becoming too saturated and causing print defects. If you submit an RGB file to IngramSpark, it will be rejected. If you convert to CMYK but exceed the ink density limit, you may see unexpected colour results.
Colour Mode for Ebooks and Digital Distributors
For ebooks, RGB is universal. Every major ebook distributor — including BookBaby, Draft2Digital, and Smashwords — requires RGB colour mode for cover images and interior graphics. This makes sense: ebooks are consumed on screens, and screens speak RGB. Submitting a CMYK image to an ebook platform can result in flat, dull-looking colours, or in some cases, rejected files.
Amazon KDP’s ebook platform follows the same logic. For Kindle books, RGB is the correct colour mode for all images, and KDP’s publishing guidelines reflect this.
When and How to Convert Between Modes
Most professional designers work in the correct colour space from the outset — designing print covers in CMYK (for IngramSpark) and digital covers in RGB. If you are commissioning a cover, it is worth specifying your distribution platforms upfront so your designer can deliver files in the appropriate colour mode.
If you need to convert yourself, Adobe Photoshop and Affinity Photo both support CMYK conversion with colour profile management. When converting from RGB to CMYK in Photoshop, use Image → Mode → CMYK Color, and use a print-appropriate CMYK profile such as U.S. Web Coated (SWOP) v2 or Fogra39, depending on your target market. After converting, check your image for any significant colour shifts and adjust as needed before export.
Free alternatives like GIMP have more limited CMYK support and are not recommended for professional print preparation.
Why Proof Copies Matter
No colour management workflow eliminates the need for a physical proof. The gap between what you see on screen and what comes off a print press depends on your monitor’s calibration, the specific paper stock used, the printer’s ink settings, and the accuracy of your colour profile. Ordering at least one proof copy before publishing — even with a platform like KDP that handles conversion automatically — is the only reliable way to verify that your cover colours look the way you expect.
A Practical Summary
Use RGB for all ebook covers and digital distribution. Use RGB for KDP Print and let KDP handle conversion, then verify with a physical proof. Use CMYK (maximum ink density 240%) for IngramSpark print files, converted before upload. If you are publishing to both print and digital, your designer should ideally provide two separate files — one per colour mode — rather than converting a single file between modes after the fact.
