Rich black against 100% K, and why body text uses one of them

What actually happens

Black ink alone, laid on white paper at small sizes, is a clean crisp black. Add cyan, magenta and yellow underneath it and you get a denser, deeper black that is visibly darker across a large area. That is the whole reason rich black exists: single black over a big panel looks washed out and slightly grey next to a photograph. The problem is that a rich black is four inks that must land in exactly the same place, and at 9 point text they do not. The plates shift by a fraction of a millimetre, and every letter acquires a coloured fringe. So the rule is not that one black is better: it is that large solid areas want rich black and small text wants black alone, and a stylesheet that uses one value everywhere gets one of the two wrong.

Where this API stands on colour

This API renders HTML to PDF, and the colour in the output is the colour in your CSS, which is RGB. There is no colour-space option, no CMYK mode, no ICC embedding, no ink-limit control and no greyscale conversion. Two options touch colour at all and neither changes a colour value: print_background, which is on by default here and off by default in most renderers, decides whether backgrounds and background images are painted at all, and media decides whether your print stylesheet applies. Anything that converts this document into inks happens after the render, in a tool you choose, and that is where the decisions on this page are enforced.

The decisions that avoid it

Reasons rather than a description of the code. Each of these is a choice with a wrong answer, and the wrong answer usually looks correct on a screen.

• Use a single black for body text, rules, and anything below about 24 point. Registration error is invisible on a panel and obvious on a letterform.
• Use a richer black for large solid areas, display type and full-bleed panels, where the extra density is visible and the registration risk is not.
• Say which you mean in the markup rather than relying on the converter to guess. A converter turning your RGB black into four-colour black everywhere is a common and expensive default.
• Never set body text to a near-black such as #111111 expecting it to convert to black ink. Anything that is not pure black converts to a mixture, which is the fringing case again.
• Keep one black value for text across the whole document. Two slightly different near-blacks in the same document print as two visibly different greys.
• Where a document is going to a press, say in the handover which blacks are which. It is a two line note that saves a reprint.

In the stylesheet

Where the decision is expressible in CSS, this is what it looks like. Where it is not, the snippet says so rather than inventing a property.

:root {
  /* Text black: pure, so a converter maps it to black ink alone and
     the letterforms cannot acquire a registration fringe. */
  --ink-text: #000000;

  /* Panel black: used only on large solid areas, where the extra
     density reads and a fraction of a millimetre of shift does not. */
  --ink-panel: #0a0a0a;
}

body { color: var(--ink-text); }

/* small type: single black, always */
p, td, th, li, .footnote { color: var(--ink-text); }

/* large solid areas: the denser value */
.cover-panel { background: var(--ink-panel); }
.display-heading { color: var(--ink-panel); font-size: 42pt; }

/* The mistake this avoids: a near-black body colour. #111 is not black,
   it is a mixture, and at 9pt a mixture fringes.
   p { color: #111; }  <-- not this */

What people do instead

Setting body text to a soft near-black like #222222 because pure black looks harsh on a screen. On a screen it does. On paper it is a four-ink grey at 9 point, and every letter has a coloured edge. Screen comfort and print legibility want opposite things here, and the document is going on paper.

How to find out rather than assume

Print a page on the real device and look at the body text with a loupe or a phone camera at maximum zoom. Clean black edges mean single black. Any colour visible at the edge of a letter means the black converted to a mixture, and the fix is in the CSS value, not at the printer.

Frequently asked

Related colour and ink topics

The topics that cause each other, then the rest of the same group.