bluecoolCC0 survey name

Indigo Blue #3A18B1

Indigo Blue is a mid-tone, vivid cool color (#3A18B1; HSL 253° 76% 39%). Name from the public-domain xkcd color survey (CC0), where it was contributed as “indigo blue”.

Use cases: Trust UI · Corporate accents

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Families: Blues · Indigo Colors

Color values

FormatValue
HEX#3A18B1
RGBrgb(58, 24, 177)
HSLhsl(253, 76%, 39%)
HSVhsv(253, 86%, 69%)
OKLCHoklch(38.69% 0.214 279.7)
OKLaboklab(38.69% 0.036 -0.2114)
CMYKcmyk(67.2%, 86.4%, 0%, 30.6%)
XYZxyz(10.0048, 4.7263, 41.9715)
CIE-LABlab(25.9, 55.3, -73.2)
CIE-LCHlch(25.9, 91.8, 307.1°)
Luminance0.047 (WCAG relative)
/* Indigo Blue */ --indigo-blue: #3a18b1; color: #3a18b1; background-color: #3a18b1;

Source: xkcd color survey name (public domain, CC0). CSS keyword: indigoblue.

Collections: Jewel Tone Colors

Shade scale

Perceptual 50–950 scale, interpolated in CIE-LAB. Step 500 is the base color. Edit in the shade generator →

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950

OKLCH ramp (perceptually uniform, modern CSS)

50
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950

Shades (toward black)

#37189e #33178b #2f1679 #2b1567 #261355 #211245 #1c1034 #170c25 #0f0617 #000000

Tints (toward white)

#5631b9 #6d47c2 #825dca #9674d2 #a88ada #baa1e1 #ccb8e9 #ddcff1 #eee7f8 #ffffff

Tones (toward gray)

#3f1ea5 #432499 #45288d #462c81 #473076 #46336a #45365f #433954 #413b49 #3d3d3d

Color harmonies

Complementary

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#3A18B1
#8FB118
#3a18b1 #8fb118

Analogous

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#1843B1
#3A18B1
#8618B1
#1843b1 #3a18b1 #8618b1

Triadic

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#3A18B1
#B13A18
#18B13A
#3a18b1 #b13a18 #18b13a

Tetradic

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#3A18B1
#B11843
#8FB118
#18B186
#3a18b1 #b11843 #8fb118 #18b186

Square

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#3A18B1
#B11843
#8FB118
#18B186
#3a18b1 #b11843 #8fb118 #18b186

Split Complementary

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#3A18B1
#B18618
#43B118
#3a18b1 #b18618 #43b118

Monochromatic

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#170945
#28117B
#3A18B1
#4F25E1
#7A5BE9
#170945 #28117b #3a18b1 #4f25e1 #7a5be9

Accessibility & contrast

10.79
#3A18B1 on #FFFFFF
AA text ✓AA large ✓AAA text ✓UI 3:1 ✓
1.95
#3A18B1 on #000000
AA text ✗AA large ✗AAA text ✗UI 3:1 ✗

Best text on indigo blue

10.79
#FFFFFF text

WCAG 2.1: AA needs ≥4.5:1 for normal text, ≥3:1 for large text and UI components; AAA needs ≥7:1 / ≥4.5:1. Open the contrast checker →

Color blindness preview

Simulation using the Machado et al. (2009) physiological model, severity 1.0. This is an approximation of perception — not a medical assessment.

Normal vision
Protanopia (red-blind)
#0043B5
Deuteranopia (green-blind)
#0037AE
Tritanopia (blue-blind)
#004B69

Closest named colors

Nearest matches by CIEDE2000 perceptual distance (ΔE₀₀) across the full color database.

ColorNameΔE₀₀
Ultramarine #2000B13.35
True Blue #010FCC3.84
Mediumblue #0000CD4.14
Violet Blue #510AC94.15
Cobalt Blue #030AA74.42
Ultramarine Blue #1805DB4.92

Colors that go with indigo blue

Top matches by hue harmony, contrast and saturation compatibility.

Purpleish Blue #6140EF
1.8:1
Same hue family as indigo blue (Δh 2°) — guaranteed harmony
Bright Lilac #C95EFB
3.3:1
Analogous hue (Δh ≈28°) — neighbors on the color wheel
Orangered #FF4500
3.1:1
Triadic harmony (Δh ≈123°) — balanced three-way contrast
Orangey Yellow #FDB915
6.2:1
Split-complementary angle (Δh ≈149°) — strong but softer than direct complement
Slime Green #99CC04
5.7:1
Complementary hue (Δh ≈178°) — maximum hue contrast

Values computed from the sRGB color model. CMYK is the naive sRGB conversion without an ICC profile. RGB percentages may differ between color-managed applications.