RGB vs CMYK — switching between screen and print color models
When to author in RGB and when in CMYK, compared by additive vs subtractive mixing, gamut, print process, and submission file formats. Why an RGB → CMYK conversion typically dulls saturated colors.
Four axes that drive the decision
RGB and CMYK are not just “web vs print” — they are based on opposite ways of producing colour. Four axes do most of the heavy lifting. How colour is produced (additive mixing vs subtractive mixing) determines which colours each medium can physically reproduce. Gamut sets the limit on saturated colours like vivid greens and fluorescent pinks. Output workflow changes the requirements depending on whether the destination is a monitor, a projector, an offset printing press, or an office inkjet. Data specification ties directly to file format choices (PNG, TIFF, PDF/X-1a) and ICC profile handling.
Skipping straight to “print means CMYK, web means RGB” is where colour drift starts. The safer move is to ask what the downstream workflow actually expects. Commercial print jobs (business cards, packaging) really do need CMYK submission, but printing a document on an office inkjet is fine to keep in RGB — the driver does the conversion internally.
Side-by-side comparison
| Property | RGB | CMYK |
|---|---|---|
| Colour model | Additive (mixing light) | Subtractive (ink absorbs light) |
| Channels | R / G / B (0-255 each) | C / M / Y + K (black plate, 0-100% each) |
| Common colour space | sRGB / Display P3 / Adobe RGB | Japan Color 2001 Coated / U.S. Web Coated (SWOP) |
| Gamut (vs sRGB) | 100% (sRGB) / ~125% (Display P3) | ~70-80% (sits mostly inside sRGB) |
| Media | Monitors / phones / cameras / scanners | Paper / fabric / plastic (offset and on-demand presses) |
| Typical file formats | JPG / PNG / WebP / AVIF | TIFF / EPS / PDF (PDF/X-1a is the submission standard) |
| Standardisation | sRGB in 1996 (IEC 61966-2-1) | Process inks date to the late 19th century; ICC profiles since 1993 |
| Editor handling | Default | Photoshop Image > Mode > CMYK Color for explicit conversion |
The gamut row is the one that bites you in production. Vivid greens, neon pinks, and pure blues all sit inside the RGB gamut (especially Display P3) but fall outside CMYK and get rounded to the nearest reproducible ink mix. That is exactly what “looked great on screen, came back muddy from the printer” means, and the rounding is one-way — once a colour is clipped to the CMYK gamut, you cannot recover the original RGB value.
Use case → recommended model
Web, apps, video, social posts: RGB (sRGB). Display P3 displays are everywhere now, but the safe default is to master in sRGB and treat P3 as an optional upgrade — most browsers and phones still assume sRGB if the file is untagged.
Commercial printing (flyers, business cards, packaging, books): submit as CMYK. The print shop will specify an ICC profile (Japan Color 2001 Coated in Japan, U.S. Web Coated v2 in North America), and the standard export is PDF/X-1a. Submitting raw RGB files means the shop converts them on your behalf, which is the most common cause of unexpected colour shifts.
Office printers and home inkjets: leave files in RGB. The printer driver internally converts to a 4-to-8-ink CMYK + light-cyan/light-magenta system, so converting yourself first only narrows the gamut.
Logos for cross-channel use: keep both an RGB master (for the website hero, email signatures, slides) and a CMYK variant (for printed collateral). Brand guidelines typically list HEX, RGB, and CMYK values side by side for this reason.
Working with colour in the browser / pitfalls
Colour conversion and contrast verification fit cleanly into a browser-only workflow. color-converter converts HEX, RGB, HSL, and OKLCH back and forth and outputs an approximate CMYK value (without an ICC profile this is an estimate, useful for sanity-checking rather than for print submission). For accessibility work, color-contrast-checker tells you instantly whether a pair of colours meets WCAG AA or AAA contrast thresholds.
Three traps catch people in practice. First, RGB → CMYK conversion is destructive: out-of-gamut colours get clipped and cannot be recovered. Always master in RGB and derive CMYK at export time. Second, monitor calibration matters more than people expect — picking colours on an uncalibrated display is the easiest way to ship a printable PDF that does not match the screen, so book a hard-copy proof for anything brand-critical. Third, transparent objects and spot colours (DIC, PANTONE) get flattened into process colours under PDF/X-1a; if you need spot inks, you have to ship PDF/X-4 or call them out in a separate spec sheet. The source is auditable on GitHub, and the DevTools Network tab confirms that no colour data leaves the page.