Blue Hour

What was measured

Closest neighbours

ΔE00 12.5

how alike two adjacent swatches look

Darkest to lightest

8.56:1

WCAG contrast across the set

Lightness covered

55 pts

of OKLCH lightness, 0–100

Under colour blindness

ΔE00 11.5

worst under deuteranopia

These two are one colour to a reader with deuteranopia. Fine while the set is read as an order; never use them to mean two different things without a label or an icon as well.

Five colours are not an interface, so this is an offer rather than a token set. It does not clear WCAG AA on the accent — stated here rather than left for you to discover.

/* Blue Hour — Interfaces that open at dusk and stay open; the top step is a usable surface. */
:root {
  --palette-1: #1c1932;
  --palette-2: #333c64;
  --palette-3: #486691;
  --palette-4: #7091ac;
  --palette-5: #a2bcc8;

  /* A suggested mapping, not a token set. It falls short of WCAG AA on the accent — fix that before shipping. */
  --bg: #a2bcc8;
  --text: #1c1932;        /* 8.56:1 on --bg */
  --muted: #333c64;      /* 5.36:1 on --bg */
  --accent: #486691;     /* 2.95:1 on --bg */
  --accent-text: #ffffff;
}

// tailwind.config — Blue Hour
export default {
  theme: {
    extend: {
      colors: {
        bluehour: {
        100: "#1c1932",
        200: "#333c64",
        300: "#486691",
        400: "#7091ac",
        500: "#a2bcc8",
        },
      },
    },
  },
};

Use the Blue Hour palette: #1C1932, #333C64, #486691, #7091AC, #A2BCC8.

It is for this: Interfaces that open at dusk and stay open; the top step is a usable surface.

Map it as ground #A2BCC8, body text #1C1932, secondary text #333C64, and one accent #486691 with #FFFFFF printed on it. That mapping does not clear WCAG AA on the accent — body 8.56:1, secondary 5.36:1, accent 2.95:1. Fix the named role against the ground before shipping; do not ship the pair as given.

Do not use it for: Print — the range collapses on paper.

Do not add a sixth colour, do not tint the greys toward a second hue, and do not carry meaning on hue alone — once colour vision is taken away the closest two of these sit only 11.5 apart on the CIEDE2000 scale, which is too close to tell apart, so pair every coloured state with a label or an icon.

How this palette was built · no hex was chosen by hand

The catalog states a recipe — ramp from hue 258 — and the five colours are derived from it in OKLCH, where a step of lightness is a step your eye agrees with rather than one the hex numbers agree with. That is why the numbers above are properties of this palette rather than claims about it.

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