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Noble Celtic Ultramarine

#3665c9
Notes

Noble Celtic Ultramarine (#3665C9) is a true azure with a cool character. It leans cool, sitting on the blue, green, and violet side of the wheel. Quiet and dependable, a fit for product UI and data visualization. Its HSL profile (221°, 58%, 50%) places it in the balanced band at a mid lightness. It works across type, buttons, and borders, saturated enough to feel deliberate but balanced enough to not fight the rest of the palette. For a confident two-color system, pair it with its complementary amber. For something softer, pull in its analogous neighbors on either side of the wheel.

HEX
#3665c9
RGB
rgb(54, 101, 201)
HSL
hsl(221, 58%, 50%)
HWB
hwb(221 21% 21%)
OKLCH
oklch(52.9% 0.164 263.1)
P3
color(display-p3 0.2563 0.3916 0.7623)
HSV
hsv(221, 73%, 79%)
LAB
lab(44.67% 18.62 -56.71)
LCH
lch(44.67% 59.68 288.17)
CMYK
cmyk(73%, 50%, 0%, 21%)

Etymology

Noble
adjective

Latin nōbilis, well-known / illustrious — sharing root with gnōscere (to know). As a color modifier, noble implies a saturated-and-dignified-and-aristocratic quality, the deep-rich color of pre-modern European noble-class hereditary-aristocratic livery-and-armorial bearings. Sits at the bold-and-aristocratic end of the grid, parallel to aristocratic and highborn in usage.

Celtic
modifier

Latin Celticus, of-the-Celts. As a color modifier, celtic implies a knotwork-and-La-Tène quality, the visual register of Irish-and-Welsh-and-Scottish Celtic-knotwork hand-carved bronze-and-stone metalwork-and-illuminated-manuscript surfaces under Celtic-Irish-Welsh-Scottish illuminated-manuscript-tradition light. Sits at the modifier-and-cultural end of the grid, parallel to norse and welsh in usage.

Ultramarine
noun

The pigment ground from lapis lazuli — the Afghan mineral imported through Venice in the late Middle Ages, more expensive by weight than gold during the Renaissance. The color refers to a freshly mixed ultramarine pigment in linseed oil: a saturated, slightly violet-shifted deep blue with the matte finish of micron-ground rock. Deeper than cobalt, cooler than royal, with the art-historical weight of the blue Vermeer reserved for Mary's robe.

Closest matches

The nearest named color in three reference sources, ranked by perceptual distance (ΔE76 in CIELAB). ΔE < 1 is imperceptible to most viewers; ΔE > 10 is clearly different. When two sources point to the same hex they’re merged into one tile; click any to open that color’s page.

Variations

Click any swatch to explore

Harmonies

Accessibility

Color-vision simulation

How this color appears to viewers with the four major color-vision-deficiency types. Computed via the Machado (2009) physiologically-based model. If a tile matches the original, the color reads the same to that viewer.

#3665c9
Original
#2a71cd
Protanopia
#0063c7
Deuteranopia
#007d8d
Tritanopia
#626262
Achromatopsia
WCAG contrast

The color used as foreground text against pure white and pure black, with the contrast ratio and WCAG 2.1 grade. Aim for AA (4.5:1) for body text and AA Large (3:1) for 18 pt+ headlines; AAA (7:1) is the gold standard for long-form reading surfaces.

The quick brown foxSample body text at normal size. The wcag minimum for body contrast is 4.5:1 (AA) or 7:1 (AAA).
AAon White
5.44:1
The quick brown foxSample body text at normal size. The wcag minimum for body contrast is 4.5:1 (AA) or 7:1 (AAA).
AA Largeon Black
3.86:1

Wide gamut

Display P3 representation

The CSS Color 4 wide-gamut form of this color. Both swatches render the same color on every display — the P3 form only diverges from sRGB when a designer pushes channels outside sRGB's reach.

sRGB hex
sRGB hex
##3665C9
Display P3
Display P3
color(display-p3 0.2563 0.3916 0.7623)
P3 has subtle headroomOKLCH chroma 0.164

Moderately saturated colors gain a small bump in P3 — the difference is usually visible side-by-side on wide-gamut hardware but won't change the character of the color.

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