What is CMYK?

Cyan, magenta, and yellow are the subtractive primary colors used in process printing. Printers add black (the K, or key) as a fourth ink because mixing the other three at full strength produces only a dark, imperfect black, while a dedicated black ink prints sharper text, gives more consistent dark tones, and costs less. The RGB (red, green, and blue) color model works the opposite way: it mixes light instead of ink, and combining all three primaries at full strength makes white.

How CMYK printing works

CMYK is a subtractive model. The white in a printed image is the paper itself, and each ink absorbs (subtracts) part of the light reflecting off it, so more ink means a darker color and no ink means white.

A press can't blend inks the way a screen blends light, so it uses halftoning: tiny dots of the four inks, varied in size and spacing, that read as smooth tones at normal viewing distance. About 20% magenta coverage reads as pink rather than full-strength magenta. Without halftone dots, solid layers of the three colored inks could produce only 8 colors: cyan, magenta, yellow, red, green, blue, a dark near-black from all three, and the white of the paper.

A CMYK value is written as four ink percentages from 0 to 100. For example, 100/0/0/0 is pure cyan, 0/100/100/0 is red, and 0/0/0/100 is plain black.

CMYK vs. RGB

CMYK is the color model for print; RGB is the color model for screens.

• CMYK: ink pigments on paper. Subtractive, so colors combine toward black. It's the standard model for color printing.
• RGB: emitted light. Additive, so colors combine toward white. Use it for anything viewed on a screen; on the web, RGB colors are usually written as hex codes.

Converting RGB designs for print

To convert an RGB design for print, first ask the printer what file format and color profile it wants. Some print shops supply an ICC profile, a file that describes a specific printing device, and want a CMYK file converted to it before you send anything; others, including many photo labs and online print services, ask for RGB files and handle the conversion in their own workflow.

Screens can generally display a wider range of colors (a larger gamut) than CMYK inks can reproduce, and the two gamuts don't fully overlap, so vivid on-screen colors, especially neon greens and bright blues, come out duller when a file is converted for print. That shift is a limit of ink on paper, not a defect in your software.

When a printer does ask for CMYK, install the ICC profile it supplies, then convert a copy of the file to that exact profile. In Photoshop, choose Edit > Convert to Profile, set the printer's profile as the Destination Space, and keep any conversion settings the shop specifies. The quicker Image > Mode > CMYK Color converts to whatever generic working profile your color settings hold, which may not match the printer's press. Either way, colors the inks can't reproduce shift to the nearest printable match.

Don't have Adobe software? The free image editor GIMP can export an RGB file to a CMYK TIFF, JPEG, or PSD as of version 3.0, released March 2025, and choosing a print service that accepts RGB files avoids the conversion entirely. Keep your RGB master untouched, and order a printed proof before a full run whenever color accuracy matters.

When a website owner needs CMYK

A website owner needs CMYK only when a design leaves the screen.

• Work in RGB and hex for anything viewed on a screen: your website, social graphics, email, and digital ads.
• Plan for CMYK when the design will be professionally printed: business cards, brochures, packaging, and signage. Check the printer's file and color-profile requirements before you convert, since many services want RGB files and convert in-house.
• Keep logos and brand colors in a master file with both RGB and CMYK values, so the brand stays as consistent as each medium allows. When an exact match matters, order a printed proof or specify a spot color.