The blue you chose on screen cannot be printed

Why the client says the colour is wrong

Your screen makes colour by emitting red, green and blue light and adding them. Paper makes colour by absorbing it: cyan, magenta, yellow and black inks each subtract part of the spectrum, and what bounces back is what you see. Two different physical processes, and the printable set is smaller.

So some colours have no CMYK recipe. Pure RGB blue (0, 0, 255), saturated orange, vivid green and every neon come back dull and grey. Nothing warned you; the file simply printed wrong.

What to do:

• Soft proof. Illustrator and Photoshop: View > Proof Colors, Ctrl+Y, with a CMYK profile set; Photoshop's Gamut Warning greys out unprintable areas. Inkscape's press colour management has historically been thin, so proof in Scribus instead.
• Better: choose colours from printed paper. Pick from a swatch book or the shop's printed CMYK chart and note the values. That removes the screen from the decision entirely.

Spot colours, and when they are worth it

A spot colour is an ink mixed to a recipe and printed from its own plate rather than simulated from four process inks. Use one when a brand colour must match across ten suppliers, when the job is one or two colours and plates beat full process, or when you need a metallic, fluorescent or very saturated colour CMYK cannot reach. Each spot is another plate, so on a full-colour job convert spots to process unless the client is paying.

Pantone's libraries left Adobe in 2022 for a paid plug-in, and the books are expensive. Most small shops work from their own printed CMYK charts, which is legitimate and costs nothing.

Bleed, trim, safe area

Three rectangles, and confusing them is the commonest print mistake.

• Trim is the finished size. A visiting card's trim is 90 × 54 mm.
• Bleed is artwork extended *past* the trim, normally 3 mm in India and Europe or 0.125 in in the US, because a guillotine cutting 500 sheets drifts by a millimetre or two. Without it, that drift shows as a white sliver along one edge — so pull a background photograph out to the bleed line, never the trim line.
• Safe area is 3–5 mm *inside* the trim. Nothing important goes there, because the same drift cuts into it. A border sitting exactly on the trim is the worst decision in print: any drift makes it visibly uneven on one side.

300 dpi, and when it is wrong

"Always 300 dpi" is a rule of thumb for images reproduced at final size at reading distance. It is wrong in both directions.

The real number comes from the halftone screen. Print reproduces tone as dots at a line screen in lines per inch, and images want roughly twice that: newspaper at about 85 lpi is fine on 170 dpi, commercial print at 150 lpi wants 300, and a hoarding seen from 50 metres is normal at 20–40 dpi full size — the same thing as building it at one-tenth scale at 300.

And vector art has no dpi at all. Do not let anyone ask you for a 300 dpi logo; ask what the finished size is.

Rich black and 100K

A large area of 100% K alone prints a washed-out dark grey, obviously weaker than a photograph's black. Rich black adds inks underneath — a common build is 60C 40M 40Y 100K.

• Total ink coverage. Add the four percentages. Presses cap it, often near 300% on coated stock and 240% on uncoated and newsprint; too much ink does not dry and offsets onto the next sheet. Ask the shop.
• Never use rich black for small text or thin lines. Four plates never register perfectly, and a fraction of a millimetre of drift puts a coloured fringe around every letter. Small text is 100K only.

Overprint, and the object that disappears

By default an object knocks out what is beneath it: the press does not lay background ink where the object sits, so the inks do not mix. Overprint switches that off and prints the object on top.

Black text is normally set to overprint, so misregistration leaves no white gap around letters.

The expensive failure: a white object accidentally set to overprint disappears completely. White in CMYK is 0/0/0/0, the absence of ink. Overprinting nothing on top of a photograph prints nothing, and the photograph shows straight through where your white logo should have been. Perfect on screen, wrong on paper.

Turn on overprint preview before every export: Illustrator's View menu, Acrobat's Output Preview, Scribus's Preview Mode.

Making the PDF the press will accept

PDF/X is a PDF with the dangerous parts forbidden: fonts embedded, colour defined, an output intent named.

• PDF/X-1a:2001 — conservative. Everything CMYK or spot, all transparency flattened. Still the default request at many shops.
• PDF/X-4 — transparency live and colour-managed, better if the shop's RIP handles it.

Ask which.

Illustrator and InDesign: Save As or Export > Adobe PDF, the [PDF/X-1a:2001] preset, then Marks and Bleeds for 3 mm bleed and offset trim marks. CorelDRAW: Publish to PDF, the PDF/X-1a or Prepress preset, bleed and crop marks on the Prepress tab. Scribus: Export > Save as PDF, bleed on the Pre-Press tab, PDF/X-3 and an output intent in the Colour tab.

The one-minute check before you send

Open your own exported PDF as if a stranger had made it:

1. 1Page size equals trim, bleed past the crop marks on all four sides, nothing important within 4 mm of trim
2. 2Zoom to 400% on small black text — 100K, not four-colour
3. 3Overprint preview on: has anything vanished?
4. 4Right pages, right order, fonts embedded

Then send it with a plain-language note — shops read this faster than any file:

Finished size 90 × 54 mm, 3 mm bleed, 4/4 colour, 300 gsm matt art card, matt lamination both sides, 500 pieces.