You designed a vibrant blue logo on screen. You printed it on a poster. The poster blue looks duller, slightly purple. You didn't change anything — except you switched from RGB to CMYK. Here's the difference and how to handle it.

RGB: how screens show color

Screens emit light. Each pixel has three tiny lights — red, green, and blue — that combine. RGB is an "additive" color model: more of all three colors = brighter, eventually white.

  • Red + Green = Yellow
  • Red + Blue = Magenta
  • Green + Blue = Cyan
  • All three at full = White
  • None = Black

RGB excels at vivid colors because the lights can shine intensely and combine without limits.

CMYK: how printing shows color

Print absorbs (rather than emits) light. Ink absorbs certain wavelengths and reflects others. CMYK uses cyan, magenta, yellow, and key (black) inks.

  • Cyan absorbs red, reflects blue and green.
  • Magenta absorbs green, reflects red and blue.
  • Yellow absorbs blue, reflects red and green.
  • Combined CMY → absorbs everything → looks dark brown (not pure black).
  • Black ink (K) added to deepen blacks (and save colored ink).

CMYK is "subtractive." Each ink subtracts colors from white paper. More ink = darker. Pure white = no ink.

Why the colors differ

Some colors that exist in RGB don't exist in CMYK. The reverse is true too. The two color models cover overlapping but not identical "color spaces" (gamuts).

Bright vivid greens and oranges look duller in CMYK. Some yellows and lavenders shift noticeably.

This is why the same design can look different on screen vs print — the colors literally cannot be reproduced exactly across both systems.

The gamut problem

Modern monitors typically use sRGB or Display-P3 color spaces. Print uses a CMYK space (typically SWOP for North American magazine print, FOGRA for European).

The print CMYK gamut is smaller — fewer colors than RGB can show. Some bright purples and electric blues don't exist in any standard CMYK setup.

How designers handle this

Three strategies:

1. Design in CMYK from the start. Use Adobe InDesign, Illustrator, or Photoshop in CMYK mode. The on-screen preview is a simulation but pretty accurate. What you see is what you'll print.

2. Design in RGB, convert to CMYK at the end. Common workflow. Conversion shifts colors slightly. Final proof checks for surprises.

3. Use Pantone (PMS) spot colors. Pantone is a separate color system used in printing. Pantone 286 is "the blue" — a specific physical ink mixture. Used for logos and brand colors that need to match exactly across applications.

The brand color problem

Many brand colors are specified differently for different media:

  • Web: hex code (#0080FF)
  • Print: CMYK percentages (100/50/0/0)
  • Spot color: Pantone reference (286 C)
  • Paint, fabric: separate color systems

A brand "blue" can be 4 different physical colors that all look similar but don't exactly match.

Practical implications

Designing for web only: stay in RGB. Hex codes, sRGB, you're done.

Designing for print only: CMYK. Most graphic design software switches modes. Use the print color picker.

Cross-media (web + print): design in RGB but check CMYK conversion. Some colors will need to be adjusted.

Important brand work: use Pantone for the few critical brand colors.

The CMYK percentages format

CMYK is described as four percentages (C/M/Y/K) from 0 to 100:

  • 0/0/0/100 = pure black
  • 0/0/0/0 = white (no ink)
  • 100/0/0/0 = pure cyan
  • 0/100/0/0 = pure magenta
  • 100/100/100/0 = brown-black (theoretical)
  • 40/30/30/100 = "rich black" (used by designers for deeper blacks)

The "rich black" trick

Pure 100% black ink (0/0/0/100) prints as a slightly thin black. Adding small amounts of CMY to black creates "rich black" that looks deeper:

  • 40/30/30/100 — popular rich black mix.
  • Used for backgrounds, large text, and print where black needs to feel substantial.

This is why your print designer might specify "100K" vs "rich black" — they look different.

Converting between RGB and CMYK

Software handles this with profile-aware conversion. The same RGB value becomes different CMYK values depending on the printer profile (SWOP, FOGRA, etc.).

For casual conversion:

  • RGB → CMYK: a vibrant red (#FF0000) becomes ~0/100/100/0 CMYK.
  • The conversion isn't reversible — once you've converted to a smaller gamut, the original info is lost.

Softproofing

To preview how an RGB design will look in print:

  1. Open in Photoshop / Illustrator.
  2. View → Proof Setup → choose your CMYK profile.
  3. View → Proof Colors (Ctrl+Y).

The screen now shows a simulation of the printed result. Vivid colors will dim noticeably.

Online tools and services

Most online printing services (Vistaprint, Moo, FedEx Office) accept RGB files and convert internally. Their conversion may shift colors. For critical brand work, send CMYK files instead.

Convert colors

Our hex/RGB color converter handles RGB-side conversions. For RGB-to-CMYK conversions, you need software that knows your printer profile (Photoshop, Affinity Photo, GIMP with color management plugins).