Tone

What tone is

Tone is the distribution of brightness across a surface. It is measured as the luminance of the paper ground and the share of ink set against it. Every other face parameter composes against the tonal ground this parameter fixes, and the ground decides how the rest will read. The reader’s first impression of a surface is its tone. The sustained experience is every other parameter working with that tone.

Three values

value	background luminance	ink-to-paper ratio	contrast floor
predominantly-light	≥ 0.90	≤ 15%	≥ 4.5
balanced	0.40 – 0.60	15% – 40%	≥ 4.5
predominantly-dark	≤ 0.15	≤ 15%	≥ 4.5

A predominantly-light surface sets near-white paper under a small fraction of ink, and the eye reads it as a page. A balanced surface sets a mid-luminance ground under a larger share of ink, and the eye reads it as a panel. A predominantly-dark surface sets near-black paper under a small fraction of ink, and the eye reads it as a plate. Each value declares its own luminance band and its own ceiling on ink share. The contrast floor, shared across the three, is never relaxed by the brightness of the ground.

How tone is measured

Luminance is measured as WCAG relative luminance on the rendered surface, in the range zero to one. Ink-to-paper ratio is measured by pixel counting. The metric is the share of pixels carrying any mark against the total area. Contrast floor is the minimum WCAG contrast ratio between any text atom and its immediate background. The three measures are independent, and a surface must satisfy each of them to satisfy its tone.

How tone composes with colour

The colour parameter names its allowed grey share and accent share against the declared tone. A predominantly-light surface at single-accent carries 97% greys and a 3% ceiling on accents. A predominantly-dark surface at single-accent carries the same ratio. On that dark ground, greys read as near-black and the paper reads as bright. Accent never fills a shape with both dimensions greater than three pixels, and the mark-only rule holds at every tone.

Named absences

There is no twilight band, no auto tone, no system-preference tone. A surface declares one of the three values in its frontmatter, and the static validator rejects any other string at parse time. The contrast floor applies to every value and never softens in the presence of a darker or brighter ground. No value carries a soft or muted mode.