It's the most common colour conversation in printing: "It looked brighter on my screen." It did. Here's why, and what to do about it.
RGB (Red, Green, Blue) is how screens work. A monitor starts black and adds light. Mix all three at full strength and you get white. Because it's built from glowing light, RGB can produce intensely vivid colours - electric blues, neon greens, hot oranges.
CMYK (Cyan, Magenta, Yellow, Key/Black) is how presses work. Paper starts white and ink subtracts light from it. Mix more ink, get darker colour. There's no glow in a sheet of paper, so the most saturated RGB colours physically cannot be reproduced in ink.
If you supply an RGB file, it has to be converted to CMYK before it can be printed. Colours inside the shared range come through fine. Colours outside it get pulled to the nearest printable equivalent - which is why that electric blue turns slightly purple and that vivid green goes a touch dull. The conversion is automatic, but the result can drift from what you expected.
Brand colours that must match exactly - across business cards, signage, vehicle magnets and everything else - are best specified properly:
One CMYK quirk worth knowing: large areas of plain 100% black ink often print grey and patchy. The fix is "rich black" - a mix of all four inks (C:60 M:40 Y:40 K:100) that produces a deep, even black. Use rich black for backgrounds and large fills, and plain 100% K for small text.
Every job we print gets a proof before production. Remember you'll be viewing that proof on a screen - in RGB - so use it to check content and layout, and trust CMYK values and printed samples for colour. If a colour is critical, tell us and we'll work with you to get it right.
More file specs on our Artwork Setup Guide, or jump straight to an instant price on the home page.