RGB vs CMYK: Colour Mode Differences Every Buyer Should Know

If you’ve ever designed artwork for a large banner or construction hoarding in the UK, you may have come across the terms RGB and CMYK. Understanding the difference between RGB and CMYK is crucial for anyone involved in hoarding printing, from event organisers and property developers to marketers. In this guide, we’ll explain RGB versus CMYK in simple terms, highlight when to use each, and why CMYK is preferred for print (especially for those big, eye-catching hoardings). Let’s dive in!

RGB versus CMYK: Two Different Colour Worlds

At first glance, RGB and CMYK are just acronyms—but they represent two very different colour systems. In essence, RGB stands for Red, Green, and Blue, and CMYK stands for Cyan, Magenta, Yellow, and Key (Black). Here’s a quick overview of each:

• RGB (Additive Colour Model): Used for digital displays like computer monitors, smartphones, and TVs. RGB blends red, green, and blue light to generate a broad spectrum of colours. It’s called additive because adding these coloured lights together makes brighter colours—add all three at full intensity and you get white light​.
• CMYK (Subtractive Colour Model): Used for physical printing with ink on paper, vinyl, or other materials. CMYK utilises cyan, magenta, yellow, and black inks, applied in fine dots or layered patterns to produce full-colour prints. It’s subtractive because the inks absorb (subtract) light. Adding all the inks together theoretically produces black (or a muddy dark colour), and if you add none, you get the white of the paper.

  This is how your desktop printer or a large-format hoarding printer works—mixing inks to reflect colours to your eyes. For example, printing cyan + yellow makes green (by absorbing red light and leaving green and blue reflected, which our eyes perceive as green). This method is also critical when producing high-quality branding panels, where colour accuracy and consistency are essential for maintaining brand identity.

In short: RGB is for screens; CMYK is for print. As one UK print expert puts it, “The main thing to remember is that RGB is used for electronic displays and CMYK is used for printing.” Each mode is suited to its medium: RGB’s bright light-based colours shine on a monitor, while CMYK’s ink-based colours are designed to look correct on paper or panel.

CMYK vs RGB Printing: Why Print Uses CMYK (and Why It Matters for Hoardings)

When it comes to hoarding printing (or any large-scale printing), using the right colour mode is critical. In practice, virtually all professional printing in the UK uses the CMYK process for full-colour work—from simple flyers to huge outdoor banners​. Your large-format printer at the print shop is literally loaded with cyan, magenta, yellow and black inks, not red, green, and blue ink.

So, why not print in RGB? The simple answer is: printers can’t. A physical printer can only lay down inks, and those inks are CMYK. If you send an RGB image to a printer, the print software or the printer’s brain will convert it to CMYK anyway. And that automatic conversion may not always guess perfectly, leading to colour shifts. As one UK banner printer warns, “Some bright colours can appear duller or muted when we convert the colours to CMYK… Create artwork in CMYK to avoid disappointment with the outcome.” In other words, design in the colour space you’ll be printing in so you have more control over the result.

Here are a few reasons CMYK is preferred for print, especially large formats like hoardings:

• Accurate Colour Reproduction: If you’ve designed your hoarding artwork in RGB, it might look brilliant on your laptop. But when printed in CMYK, certain colours may shift. For example, a vivid RGB teal or neon orange on screen could turn out flatter in print. By designing (or converting) to CMYK beforehand, you can see and adjust those colour changes before Most printers advise saving your file in CMYK because “saving a file as RGB for print can impact how colours are printed.
  
• Consistent Brand Colours: For marketing and branding, colour consistency is key. Companies spend a lot ensuring their logo blue or campaign green looks the same everywhere. Outdoor advertising and signage (like those printed hoarding boards on UK construction sites) are almost always printed in CMYK, so understanding how your digital RGB colours travel to print is important to maintain brand consistency.
  If your brand orange falls outside the CMYK gamut, a professional can tweak the CMYK values to get the closest match so your hoarding still pops with your brand identity.
• Large Scale Magnifies Differences: Hoardings are big, often stretching many meters across site fencing. Minor colour inaccuracies that might go unnoticed on a small screen can become more apparent on a 10-meter banner.
  Using the correct CMYK vs. RGB printing approach ensures the large-format output looks as intended. Plus, large-format printers are high-end machines that assume files are prepared correctly. Feeding them the proper CMYK artwork helps take full advantage of their capabilities (like high resolution and colour fidelity).
• Print Industry Standard: Simply put, CMYK is the standard colour model in printing. In today’s thriving print industry, virtually all print companies require artwork prepared in the CMYK format for full-colour projects.
  It’s a common requirement in artwork guidelines to “convert all RGB colours to CMYK” before sending files to print​. Following this standard saves time (and potential extra charges) in the print production process.

Why Hoarding Print Buyers Should Care (Accuracy = Impact)

If you’re planning to purchase or commission a hoarding print, having a clear understanding of CMYK vs. RGB printing will enable more effective communication with your designers and printers, leading to a more accurate final output. When you know that CMYK is the language of printers, you can ensure your designer supplies the artwork correctly. This avoids delays or unintended colour shifts. It’s all about accurate colour reproduction. The last thing you want is your carefully chosen event artwork looking different on the hoarding panels than it did in the promo materials!

There’s also an economic angle: high-quality print materials can offer a great return on investment. Print marketing in the UK remains powerful—in fact, studies show print advertising can yield £6.36 in profit for every £1 spent  , a higher ROI than TV or digital media​. That kind of impact only happens when the print looks right. A well-produced, colour-accurate hoarding can grab attention from passers-by and convey professionalism, whereas off-colour or dull imagery might not achieve the same effect. So, getting the colours right (by using CMYK properly) has real benefits for your campaign’s success.

Conclusion

In summary, RGB and CMYK colours serve different purposes: RGB for vibrant on-screen graphics and CMYK for reliable in-print results. For hoarding printing—and all large-scale print jobs—CMYK is the way to go to ensure your design’s colours come out as expected in the real world.

Ready to turn your bright ideas into a bold hoarding? Ensure your artwork is print-ready and let a professional make it happen. If you have an upcoming project or want to see your designs splashed across a big, beautiful hoarding, get in touch with our expert team today. Contact us for a friendly chat or request a quote—we’re here to help bring your vision to life in full colour (the right colour!). Let’s create something amazing together.