Blue vs. Indigo - What's the difference?

Main Difference

The main difference between Blue and Indigo is that the Blue is a color; additive and subtractive (RYB) primary color; visible between purple and green and Indigo is a deep and bright shade of blue.


Blue is one of the three primary colours of pigments in painting and traditional colour theory, as well as in the RGB colour model. It lies between violet and green on the spectrum of visible light. The eye perceives blue when observing light with a dominant wavelength between approximately 450 and 495 nanometres. Most blues contain a slight mixture of other colors; azure contains some green, while ultramarine contains some violet. The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. An optical effect called Tyndall scattering explains blue eyes. Distant objects appear more blue because of another optical effect called atmospheric perspective. Blue has been an important colour in art and decoration since ancient times. The semi-precious stone lapis lazuli was used in ancient Egypt for jewellery and ornament and later, in the Renaissance, to make the pigment ultramarine, the most expensive of all pigments. In the eighth century Chinese artists used cobalt blue to colour fine blue and white porcelain. In the Middle Ages, European artists used it in the windows of Cathedrals. Europeans wore clothing coloured with the vegetable dye woad until it was replaced by the finer indigo from America. In the 19th century, synthetic blue dyes and pigments gradually replaced mineral pigments and synthetic dyes. Dark blue became a common colour for military uniforms and later, in the late 20th century, for business suits. Because blue has commonly been associated with harmony, it was chosen as the colour of the flags of the United Nations and the European Union.Surveys in the US and Europe show that blue is the colour most commonly associated with harmony, faithfulness, confidence, distance, infinity, the imagination, cold, and sometimes with sadness. In US and European public opinion polls it is the most popular colour, chosen by almost half of both men and women as their favourite colour. The same surveys also showed that blue was the colour most associated with the masculine, just ahead of black, and was also the colour most associated with intelligence, knowledge, calm and concentration.


Indigo is a deep and rich color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine. It is traditionally regarded as a color in the visible spectrum, as well as one of the seven colors of the rainbow: the color between violet and blue; however, sources differ as to its actual position in the electromagnetic spectrum. The color indigo is named after the indigo dye derived from the plant Indigofera tinctoria and related species. The first known recorded use of indigo as a color name in English was in 1289.

Blue vs. Indigo


Table of contents

1. Alternative forms
          3.1. Adjective
                    3.1.1. Antonyms
          3.2. Descendants
          3.3. Noun
                    3.3.1. Further reading
          3.4. Verb
          3.5. See also
          4.1. Adjective


1. Alternative forms

  • blew (obsolete)
  • blewe (obsolete)

2. Pronunciation

  • enPR: blo͞o, IPA(key): /bluː/
  • (General American) IPA(key): /blu/
  • Rhymes: -uː
  • Homophone: blew

3. Etymology 1

From Middle English blewe, partially from Old English *blǣw ("blue"; found in derivative blǣwen (bluish)); and partially from Anglo-Norman blew, blef (blue), from Old Frankish *blāw, *blāo (blue) (perhaps through a Medieval Latin blāvus, blāvius (blue)); both from Proto-Germanic *blēwaz (blue, dark blue), from Proto-Indo-European *bʰlēw- (yellow, blond, grey). Cognate with dialectal English blow (blue), Scots blue, blew (blue), North Frisian bla, blö (blue), Saterland Frisian blau (blue), Dutch blauw (blue), German blau (blue), Danish, Norwegian and Swedish blå (blue), Icelandic blár (blue), Latin flāvus (yellow), Middle Irish blá (yellow), Lithuanian blãvas (blue). Doublet of blae.

3.1. Adjective

blue (comparative bluer, superlative bluest)

  1. Of the colour blue.
  2. (informal) Depressed, melancholic, sad.
    • “Heavens!” exclaimed Nina, “the blue-stocking and the fogy!—and yours are pale blue, Eileen!—you’re about as self-conscious as Drina—slumping there with your hair tumbling à la Mérode! Oh, it's very picturesque, of course, but a straight spine and good grooming is better. []
    • 1904, Guy Wetmore Carryl, The Transgression of Andrew Vane, Henry Holt and Company, page 140:
      "Will you play some of the 'Garden' now?" she asked. "I think I should like it. I'm just the least bit blue."
  3. Pale, without redness or glare; said of a flame.
  4. (politics) Supportive of, run by (a member of), pertaining to, or dominated by a political party represented by the colour blue.
    1. (politics, in particular, in the US) Supportive of, run by (a member of), pertaining to, or dominated by the Democratic Party. [after 2000]
    2. (Australia, politics) Supportive of or related to the Liberal Party.
  5. (astronomy) Of the higher-frequency region of the part of the electromagnetic spectrum which is relevant in the specific observation.
  6. (of steak) Extra rare; left very raw and cold.
  7. (of a dog or cat) Having a coat of fur of a slaty gray shade.
  8. (archaic) Severe or overly strict in morals; gloomy.
  9. (archaic, of women) literary; bluestockinged.
    • (Can we date this quote?) William Makepeace Thackeray
      The ladies were very blue and well informed.
  10. (particle physics) Having a color charge of blue.
  11. (entertainment) Risque or obscene

3.1.1. Antonyms

  • (having blue as its colour): nonblue, unblue
  • (having blue as its colour charge): antiblue

3.2. Descendants

  • Tok Pisin: blu
  • Fiji Hindi: bulu
  • Shona: bhuluu
  • Somali: buluug
  • Swahili: bluu, buluu

3.3. Noun

blue (countable and uncountable, plural blues)

  1. (countable and uncountable) The colour of the clear sky or the deep sea, between green and violet in the visible spectrum, and one of the primary additive colours for transmitted light; the colour obtained by subtracting red and green from white light using magenta and cyan filters; or any colour resembling this.
    • 2004, David Mitchell, Cloud Atlas
      She watches the yachts in the creamy evening blues.
  2. A blue dye or pigment.
  3. Any of several processes to protect metal against rust.
  4. Blue clothing
    The boys in blue marched to the pipers.
  5. (in the plural) A blue uniform. See blues.
  6. (slang) A member of law enforcement
  7. The sky, literally or figuratively.
    The ball came out of the blue and cracked his windshield.
    His request for leave came out of the blue.
  8. The ocean; deep waters.
  9. Anything blue, especially to distinguish it from similar objects differing only in color.
  10. (snooker) One of the colour balls used in snooker, with a value of 5 points.
  11. Any of the butterflies of the subfamily Polyommatinae in the family Lycaenidae, most of which have blue on their wings.
  12. A bluefish.
  13. (Australia, colloquial) An argument.
    • 2008, Cheryl Jorgensen, The Taint, page 135,
      If they had a blue between themselves, they kept it there, it never flowed out onto the streets to innocent people — like a lot of things that have been happenin′ on the streets today.
    • 2009, John Gilfoyle, Remember Cannon Hill, page 102,
      On another occasion, there was a blue between Henry Daniels and Merv Wilson down at the pig sale. I don′t know what it was about, it only lasted a minute or so, but they shook hands when it was over and that was the end of it.
    • 2011, Julietta Jameson, Me, Myself and Lord Byron, unnumbered page,
      I was a bit disappointed. Was that it? No abuse like Lord Byron had endured? Not that I was wishing that upon myself. It was just that a blue between my parents, albeit a raging, foul, bile-spitting hate fest, was not exactly Charles Dickens.
  14. A liquid with an intense blue colour, added to a laundry wash to prevent yellowing of white clothes.
  15. (Britain) A type of firecracker.
  16. (archaic) A pedantic woman; a bluestocking.
  17. (particle physics) One of the three color charges for quarks.

3.3.1. Further reading

  • Blue (colour) on Wikipedia.Wikipedia

3.4. Verb

blue (third-person singular simple present blues, present participle blueing or bluing, simple past and past participle blued)

  1. (ergative) To make or become blue.
  2. (transitive, metallurgy) To treat the surface of steel so that it is passivated chemically and becomes more resistant to rust.
  3. (transitive, laundry) To brighten by treating with blue (laundry aid)
  4. (transitive, slang) To spend (money) extravagantly; to blow.
    • 1974, GB Edwards, The Book of Ebenezer Le Page, New York 2007, page 311:
      They was willing to blue the lot and have nothing left when they got home except debts on the never-never.

3.5. See also

  • (blues) blue; Alice blue, aqua, aquamarine, azure, baby blue, beryl, bice, bice blue, blue green, blue violet, blueberry, cadet blue, Cambridge blue, cerulean, cobalt blue, Copenhagen blue, cornflower, cornflower blue, cyan, Dodger blue, duck-egg blue, eggshell blue, electric-blue, gentian blue, ice blue, lapis lazuli, lovat, mazarine, midnight blue, navy, Nile blue, Oxford blue, peacock blue, petrol blue, powder blue, Prussian blue, robin's-egg blue, royal blue, sapphire, saxe blue, slate blue, sky blue, teal, turquoise, ultramarine, Wedgwood blue, zaffre
  • bluing (steel) on Wikipedia.Wikipedia
  • Havasupai
  • primary colour
  • rainbow
  • RGB

4. Etymology 2

From the color of the envelopes used to contain missives of the censors and managers to vaudevillian performers on objectionable material from their acts that needed to be excised.

4.1. Adjective

blue (comparative more blue, superlative most blue)

  1. (entertainment, informal) Pornographic or profane.

5. Anagrams

  • Buel, lube


1. Etymology

16th century (as indico, modern spelling from the 17th century), Spanish índigo, Portuguese endego (modern índigo), or Dutch (via Portuguese) indigo, all from Latin indicum (indigo), from Ancient Greek Ἰνδικὸν (Indikòn, Indian dye), from Ἰνδία (Indía).

2. Pronunciation

  • (UK) IPA(key): /ˈɪn.dɪˌɡəʊ/
  • (US) IPA(key): /ˈɪndɪˌɡoʊ/

3. Noun

indigo (countable and uncountable, plural indigos or indigoes)

  1. A purplish-blue colour
  2. An indigo-colored dye obtained from certain plants (the indigo plant or woad), or a similar synthetic dye.
  3. An indigo plant, such as from species in genera Indigofera, Amorpha (false indigo), Baptisia (wild indigo), and Psorothamnus and Dalea (indigo bush).

4. Adjective

indigo (comparative more indigo, superlative most indigo)

  1. having a deep purplish-blue colour

5. References

More Comparisons