Blue4
blue4 · #00008B
HEX
#00008B
RGB
rgb(0, 0, 139)
CMYK
cmyk(100%, 100%, 0%, 45%)
HSL
hsl(240, 100%, 27%)
LAB
lab(14.8, 50.4, -68.7)
What is Blue4?
Blue4 is the blue4 reference in the X11 named colors. Its sRGB value is #00008B (rgb 0, 0, 139). It sits in the blue family. Historical X Window System color names — the numbered 1-4 lightness variants of the classic xorg-server rgb.txt palette. See disclaimer for accuracy and trademark notes.
Accessibility
WCAG 2.1 contrast checks for Blue4 as a background.
Black text on this color
White text on this color
Shades, tints & tonal scale of Blue4
An 11-step tonal scale derived from Blue4 (#00008B). Click any swatch to copy its HEX. Use these as a starting point for design tokens, hover states, and disabled states in a design system.
50
#EBEBF6
#EBEBF6
100
#D6D6EC
#D6D6EC
200
#ADADDA
#ADADDA
300
#8080C5
#8080C5
400
#4040A8
#4040A8
500
#00008B
#00008B
600
#000076
#000076
700
#00005A
#00005A
800
#00003F
#00003F
900
#000023
#000023
950
#000011
#000011
Lighter tints (mixed with white)
15%
#6C6CA4
30%
#9595B8
45%
#B3B3CA
60%
#CBCBDA
75%
#E1E1E9
Darker shades (mixed with black)
15%
#000081
30%
#000076
45%
#000069
60%
#00005A
75%
#000048
Color harmonies for Blue4
Classic color-theory harmonies derived from rotating the hue of Blue4. Use these to build accent palettes, brand systems, and accessible UI color pairings.
Complementary
180° opposite — strongest contrast
#00008B
#00008B
#8A8A00
#8A8A00
Triadic
Three colors 120° apart
#00008B
#00008B
#8A0000
#8A0000
#008A00
#008A00
Analogous
Two neighbors ±30° on the wheel
#00458A
#00458A
#00008B
#00008B
#45008A
#45008A
Split-complementary
Base + two colors flanking its complement
#00008B
#00008B
#8A4500
#8A4500
#458A00
#458A00
Tetradic
Two complementary pairs
#00008B
#00008B
#8A008A
#8A008A
#8A8A00
#8A8A00
#008A00
#008A00
Square
Four colors evenly spaced 90° apart
#00008B
#00008B
#8A0045
#8A0045
#8A8A00
#8A8A00
#008A45
#008A45
Blue4 in every color space
Full conversion of Blue4 across the color spaces designers and developers actually use — including OKLCH (the perceptually-uniform space that powers Tailwind v4 and CSS Color Module Level 4) and HWB.
HEX
#00008B
RGB
rgb(0, 0, 139)
CMYK
cmyk(100%, 100%, 0%, 45%)
HSL
hsl(240, 100%, 27%)
HSV
hsv(240, 100%, 55%)
HWB
hwb(240 0% 45%)
CIE Lab
lab(14.8 50.4 -68.7)
OKLCH
oklch(28.8% 0.199 264.1)
XYZ (D65)
xyz(4.66, 1.86, 24.54)
Copy-ready code for Blue4
Drop-in snippets for CSS, Tailwind, Sass, iOS Swift, and Android XML. Click the copy button on any snippet to put it on your clipboard.
CSS
color: #00008B;
background-color: #00008B;CSS variable
:root {
--color-blue4: #00008B;
}Tailwind config
// tailwind.config.js
colors: {
'blue4': '#00008B',
}Sass
$color-blue4: #00008B;Swift UIColor
UIColor(red: 0.000, green: 0.000, blue: 0.545, alpha: 1.0)Android XML
<color name="blue4">#00008B</color>Closest match in every color system
The nearest Blue4 equivalent in every other color system on this site, ranked by ΔE2000 perceptual distance. Useful when translating between design-system, web-standard, and industrial color references.
Closest in X11 named colors
Top 6 ΔE2000-closest entries within the same collection.
Closest Pantone matches
Top 6 ΔE2000-closest Pantone references. Cross-system matching is approximate — see disclaimer.
Closest RAL Classic matches
Top 6 ΔE2000-closest RAL Classic references for industrial coating cross-reference.
RAL 5005
#1E2460
Signal blue
RAL 5002
#20214F
Ultramarine blue
RAL 5020
#1D334A
Ocean blue
RAL 5022
#252850
Night blue
RAL 5010
#0E294B
Gentian blue
RAL 5017
#063971
Traffic blue
FAQ about Blue4
What is the HEX code for Blue4?
Blue4 (blue4) has the HEX code #00008B. In RGB it is rgb(0, 0, 139), and in CMYK it is cmyk(100%, 100%, 0%, 45%).
What is the OKLCH value of Blue4?
Blue4 converts to oklch(0.288 0.199 264.1). OKLCH is the perceptually uniform color space used by Tailwind v4 and CSS Color Module Level 4.
Is Blue4 accessible for body text?
Used as a background, Blue4 has a contrast ratio of 1.37:1 with black text and 15.30:1 with white text. WCAG 2.1 AA requires 4.5:1 for normal text. The current recommendation is to use white text and verify in real UI context.
What is the closest Pantone to Blue4?
The closest Pantone reference to Blue4 by ΔE2000 perceptual distance is Pantone Reflex Blue C (#001489). Cross-system Pantone matching is approximate; for color-critical print work, verify with a physical Pantone guide.
What is the closest RAL color to Blue4?
The closest RAL Classic reference to Blue4 by ΔE2000 distance is RAL 5005 (Signal blue, #1E2460). RAL is a German industrial coating standard commonly used for paint, powder coat, and architectural specification.
What is the complementary color of Blue4?
The complementary color (180° opposite on the HSL color wheel) of Blue4 is #8A8A00. Use it for high-contrast accents, error states, or call-to-action pairings.
Data provenance & source
X11 named colors (xorg rgb.txt)
The historical X11 color name list shipped in the xorg-server rgb.txt file. Roughly 550 entries covering classic computing color names like 'PapayaWhip', 'MediumAquamarine', and 'DarkSlateGray'. Many CSS named colors originate here. Use as a reference for legacy and creative color names. Most modern CSS implementations accept these names directly.
- Source type
- derived
- Confidence
- high
- License
- MIT/X11 license (X Consortium)
- Last reviewed
- 2026-05-24
Workflow tags
X11 colors are sRGB digital values from a 1980s color system. For print, convert to a process-appropriate color and proof against substrate.