Often, I have to decide whichever is better in mail, forums, letters. For instance:

  • colour vs color
  • flavour vs flavor
  • behaviour vs behavior
  • humour vs humor
  • rumour vs rumor
  • honour vs honor
  • armour vs armor

The difference comes certainly from the country of origin of the writer — basically Americans write o and English people write ou. Please confirm that.

(By the way, all the words left side are underlined in Firefox, since the spell-checker is set to “American English”)

What I would like to know — from a non-native English speaker's perspective — does it really matter, nowadays with the new technologies and international exchanges, to make a distinction between "ou" and "o"?

Does it hurt the reader if they are both used in the same text, mixing colour and honor, or even worse, colour and color?

What is the current trend?

  • 2
    Possible duplicate
    – Kosmonaut
    Commented Jan 3, 2011 at 16:43
  • 1
    @Kosmonaut I don't agree on the question being a duplicate of colour vs color. I'm more interested in the current trend, "o" vs "ou".
    – Déjà vu
    Commented Jan 3, 2011 at 16:50
  • 2
    That's why I wrote "possible" instead of closing it :)
    – Kosmonaut
    Commented Jan 3, 2011 at 16:51
  • I'm a German and I use an US-English spell-checker in Firefox.
    – bernd_k
    Commented Jan 3, 2011 at 16:52
  • english.stackexchange.com/questions/4474/… might be relevant.
    – ukayer
    Commented Feb 23, 2011 at 4:34

5 Answers 5


You're correct that "o" is US and "ou" is non-US. It'd be considered bad style to switch between them in the same text. Generally, you should just choose one style and use it consistently, and you will be understood. I've heard a rule that if you're writing for a mostly American audience, you should use the American spelling, and otherwise use the international forms, but that may not even be necessary.

One place that mixing styles is allowed is when quoting verbatim from text, or in technical literature where spellings must be retained exactly:

I asked him what colour he wanted, and he said "I'm no good at picking colors".

The color: #ffffff; property indicates a text colour of white.

  • 1
    In I asked him what colour he wanted, and he said "I'm no good at picking colors" it is beyond subtly to use the change of spelling simply to imply an American accent for the whole phrase.
    – Henry
    Commented Mar 19, 2011 at 13:14
  • 1
    @Henry: I wasn't talking about accents (though that is a neat idea to tuck away for later). I was referring to quoting a passage from an email, for example, or any context where it's trivial to copy verbatim, so there's no reason to put the effort into alteration.
    – Jon Purdy
    Commented Mar 22, 2011 at 0:47
  • If it’s meant to indicate copying verbatim from a text, it would be much clearer to write “he wrote” rather than “he said”. Commented Nov 22, 2023 at 14:29

As several people have stated, the 'o' form is American. You should pick a format and stick with it. If you write 'o' your writing will be perceived as American. Otherwise it will be perceived as non-American. Does that matter to you, and do you think it matters to your audience? If so, pick the appropriate style that best suits you or your writing.

As for trends, one thing I've noticed as a Canadian is that many computer programs only recognize US and UK English and not Canadian or Australian or New Zealand or.... Also the default for lots of software tends to be US. So if you want to pick the lazy, pragmatic route, the American spelling will probably be more convenient.

  • 1
    I'm just curious - how do Canadian, Australian and New Zealand spellings differ from UK spellings? Or are you referring to some other aspect of the language?
    – CPRitter
    Commented Jan 18, 2013 at 13:29
  • 1
    @CPRitter: Canadian, in particular, picks some spelling variants based on the American usage (e.g. jail, tire) and other variants based on the British usage (e.g. colour, harbour). I'm not sure to what degree Australian and New Zealand spellings differ from standard UK spellings. Commented Jan 18, 2013 at 14:06

So, first, yes, the o variations are preferred in the US while the ou variations are preferred in Commonwealth realms (at least, the ones I'm familiar with. Any counterexamples would be welcome).

As to the question of whether it matters, it depends greatly on the type of communication, the purpose, the reader, etc. While mixing and matching shouldn't hurt comprehension, as a matter of style, I would suggest consistency within a text in any formal or business-related writing, especially the color / colour type. In informal emails, forum posts, etc. I wouldn't spend a ton of time worrying with it.

As far as which you should choose, I would keep the following in mind: if you choose the reader's preferred spelling, it will likely not have any particular effect on them as they read it. However, if you choose the UK spelling for a US audience or vice versa, it will potentially be noticed as an explicit difference by the reader. This can have a couple of side-effects: it can take them out of the flow of the material, breaking up a nicely flowing sentence and distracting slightly from the content; it can also inform the reader of your background. While neither of these may matter if you're posting a question on a computer help forum, if it was a patriotic statement for a UK MP, I certainly wouldn't want it to appear to have been written by a yank, for instance.

  • Well, I didn't have a lot of correspondence with a UK MP recently... More generally, could I stick to a default strategy - I'm tempted to stick to the "o"s, isn't it the trend anyway? (thanks to the Internet)
    – Déjà vu
    Commented Jan 3, 2011 at 16:47
  • 1
    I don't see a problem picking a default strategy. This is how native speakers work, anyway. Being from the US, I use the o spellings 99% of the time, and I imagine the opposite is true for those native to the ou. As far as a trend, I'm not sure worldwide. Certainly, I rarely see ou spellings, but that may just be from my vantage point. In the UK o spellings may be as rare. And non-native English countries vary whether UK or US English is dominant. Which type is most common in the English-speaking fora you find yourself in? I'd go with that one.
    – Dusty
    Commented Jan 3, 2011 at 17:11
  • I note that the "ou" versions as well as other British English versions seem more prevalent in Europe in general.
    – Suvrit
    Commented Jan 3, 2011 at 17:30
  • 2
    In Holland, school books use British in everything, at least they did 10 years ago. And it is considered more "cultured" to use British spelling, pronunciation etc. for everything, though it doesn't matter a lot. American variants = a victim to popular culture and consumerism; British variants = cultured and traditional (much exaggerated, o.c.). In addition, European languages have always felt threatened by the pressure of the dominant foreign language, which has been French, German, and English, respectively; and since this pressure now comes strongest from Am. culture, we resist AmE most. Commented Jan 3, 2011 at 17:47
  • P.S. I was merely describing a vaguely circulating social phenomenon, not by any means stating my opinion on American and British English. Commented Jan 3, 2011 at 17:50

I'm not even going to mention the fact that "o" is American English and "ou" is British English, as it has been mentioned by every other answer. (Whoops! I just mentioned it;)

But since you asked for trends -- I've noticed that in America, "o" is used almost exclusively, except for instances where people try to sound fancy and/or formal, such as wedding invitations (as in "We request the honour of your presence.")

First hit on Google images for "wedding invitation":
wedding invitation

^^ Note that this is an American invitation; the wedding is in California ;)

  • 1
    You’re right: these things aren’t cut-and-dry. One misconception is that (for example) all ‑our or ‑re words switched over to -or or ‑er words at once. Nothing could be further from the truth, as proven in this answer to How and when did American spelling supersede British spelling in the US?. It’s only with the advent of computer-enforced delusions that there can be only one right spelling of many of these that people have been tricked into believing some Manich₍ₐ₎ean heresy of homogeneous orthographic rectitude.
    – tchrist
    Commented Jul 13, 2014 at 21:40
  • @tchrist Wow, that is one tremendous answer....+1 ;)
    – Shokhet
    Commented Jul 13, 2014 at 21:47
  • To add to @tchrist's point, note that some -our words switched before the US spelling branch. For example, tailor has generally been spelled that way since Middle English, even though it originates from a French spelling taillour. Here's the British ngram for tailor, showing it was almost always spelled that way except for a brief time in the 1580s. books.google.com/ngrams/… Commented Aug 24, 2016 at 10:04

Others have pointed out the difference, as being American vs British. You asked also about the trend. One way to get an idea, yourself, is to use Google Ngram.

If you type color and colour into it, for example, you get this graph, which shows that color seems to be gaining in usage over colour in both US English and British English. But not so, for labor vs labour.

  • 1
    Yeah, these things are tricksy. See this answer about just one sort of dodginess involved with Google N-Grams, and also this answer for more about transatlantic orthographic trends.
    – tchrist
    Commented Jul 13, 2014 at 21:43
  • Yeah, I'm glad you posted those links. I've now made them favorites, so I can easily refer to them later in such contexts. Ngram is what it is. I hope someone else will post a better indication of the trend in this case, to answer that part of the OP.
    – Drew
    Commented Jul 13, 2014 at 22:00

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