"I sent you the file and the blue came out purple!", almost always the cause is CMYK vs RGB.
Screens use RGB light, banner printers use CMYK inks. Convert your artwork to CMYK before sending, specify a Pantone for critical brand colours, and you will avoid the bright blue going purple.
Quick Summary
- Screens use RGB (Red, Green, Blue light)
- Printers use CMYK (Cyan, Magenta, Yellow, blacK inks)
- They render colour differently.
RGB vs CMYK at a Glance
| Aspect | RGB | CMYK |
|---|---|---|
| Used For | Screens, web, phones | Print, banners, signage |
| Mixing | Adds light | Subtracts with ink |
| Range | Wider, more neon | Narrower, more realistic |
| Base | Black screen | White material |
Technical (Simplified)
RGB is "additive", adding light to black. CMYK is "subtractive", adding ink to white paper. Some very bright RGB colours cannot be printed in CMYK.
If a colour glows on screen, something has to give in print. Ink cannot emit light, it can only reflect it.
Which Colours Shift Most?
- Bright reds → slightly more orange
- Electric blues → slightly more purple
- Neon greens → slightly more muted
- Fluorescent pinks/yellows → significantly duller
The Fix
Convert your file to CMYK before sending. Photoshop: Image → Mode → CMYK Color. Illustrator: File → Document Colour Mode → CMYK.
Convert in Photoshop
Image > Mode > CMYK Color. Then check any headline text or brand colour and adjust if it looks flat.
Convert in Illustrator
File > Document Colour Mode > CMYK. Update any swatches that were set in RGB values.
Fix the colour mode before you sign off the proof, not after the banner is printed. Ink is not reversible.
Pantone
For critical brand colours, specify a Pantone number.
Our Free Artwork Check
Every file sent to BPSD gets checked. If it's RGB, we flag it and show you the converted CMYK version.
Email your file or call 020 3669 9854.
