RGB vs CMYK for Printing

Screens create colour with light using RGB (red, green, blue). Most printers create colour with ink using CMYK (cyan, magenta, yellow, black). This difference is why a vivid screen colour can look duller on paper.

The short version

Design for screen (websites, social media, video): keep RGB.
Design for digital print (inkjet, laser, most print shops): RGB is usually fine because the shop converts the file automatically with their colour profiles.
Design for commercial offset printing (magazines, packaging, large runs): follow the printer's instructions, which often mean supplying CMYK files.

Why colours change

RGB is an additive colour space: combining red, green and blue light makes white, and the gamut (range of colours) is larger than ink can reproduce. CMYK is subtractive: ink absorbs light, and bright neon colours from a screen simply do not exist as ink on paper. A conversion can never add colour the printer cannot produce - it only maps to the closest printable colour.

Practical tips

Ask your print service which colour mode and profile they want before exporting.
Proof on the same paper type if colour accuracy matters, because paper brightness changes appearance.
Avoid designing with neon or very saturated screen colours if exact reproduction is important.
Use soft-proofing in Photoshop (View → Proof Setup) to preview the CMYK result before sending files.

Frequently asked questions

Do I need to convert my JPEG to CMYK before sending it to a print shop?

Usually not for digital printing. Most shops accept RGB and convert automatically. Only follow a specific CMYK request from an offset printer or a service that demands CMYK files.

Why is my printed blue or green different from my screen?

Every screen shows colour slightly differently, and CMYK ink cannot reproduce the brightest RGB blues and greens. Calibrate your monitor and ask for a physical proof when colour is critical.