# CMYK vs RGB for print: why colour shifts

> How screens and ink reproduce colour differently, which brand colours shift, and when a spot colour or a physical proof is the only way to match.

Pillar: artwork · Updated: 2026-11

**Our view.** If the brand colour lives on screens and packaging, design in CMYK and proof on the real stock. We would rather tell a customer that their neon green cannot be printed than print it dull and call it a colour difference. Spot colour exists precisely for the colours CMYK cannot reach.

A file that looks perfect on screen can print duller, darker or simply different. That is not a printing fault; it is two colour models describing different physical realities.

## Two models, two gamuts

**RGB** is light: red, green and blue added together. A screen can produce very bright, saturated colours because it emits light.

**CMYK** is ink: cyan, magenta, yellow and black subtracted from white paper. Ink absorbs light, so the printable range is smaller — especially in bright greens, oranges and deep blues.

Every colour outside the CMYK gamut is "out of gamut" and will be approximated when converted.

## The colours that shift most

| Colour | What happens in CMYK |
|---|---|
| Bright orange | Becomes duller and redder |
| Vivid green | Loses saturation, can look olive |
| Electric blue | Darkens and desaturates |
| Neon / fluorescent | Cannot be reproduced with CMYK at all |
| Metallic gold / silver | Requires a metallic stock or foil, not ink |

If a brand colour is one of these, CMYK printing will not match it — and no amount of tweaking the file will fix that.

## What to do about it

**1. Supply CMYK files.** If you send RGB, the printer converts it, and the conversion is a judgement call you did not make.

**2. Ask for a physical proof on the real material.** A screen proof cannot show how ink sits on matte paper versus gloss film.

**3. Use a spot colour when the match matters.** Flexo can print a mixed ink to a Pantone reference — exact, but a separate plate and a separate cost.

**4. Accept small variation between runs.** Print runs vary slightly in ink density; a brand colour that is "close" on one run may be slightly different on the next.

## Black text

For small text, use 100% K rather than a rich black (CMYK mixed). Rich black on small type can look blurry from registration shift, and on uncoated stock it can look muddy.

For large solid areas, a rich black gives a deeper result — a deliberate choice, not a default.

## White ink

White is not a CMYK colour. On clear or metallic stock, white is a separate ink layer printed behind the design. Without it, colours are translucent. This is why clear labels and clear stickers need a white-ink decision in the artwork, not just in the quote.

## What this means for buyers

**Design in CMYK from the start** if print is the destination; converting at the end is where surprises come from.

**Check your brand colour against a CMYK swatch** before approving a design, not after the run.

**Ask for a proof on the actual stock** when colour matters. It is the only test that includes ink, material and finish.

**Spot colour is a budget decision.** Exact match is possible; it costs a plate and a separate pass, and it is usually worth it only on high-volume brand packaging.

## Quick answers

**Why does my label look duller than my screen?**

Because screens emit light and ink absorbs it, so CMYK covers a smaller range of colour. Bright greens, oranges and deep blues fall outside it and get approximated. A physical proof on the actual stock shows what will really print.

**Can neon or metallic colours be printed?**

Not with CMYK. Neons need fluorescent inks, metallics need foil or a metallised stock. Both are separate processes with their own setup cost, and both are worth asking about before the design is finalised rather than after.

## Sources

- ISO 12647-6:2020 — Process control for flexographic printing — https://www.iso.org/standard/75219.html
- ISO 12647-7:2016 — Proofing processes working from digital data — https://www.iso.org/standard/66426.html