Consider these two phrases:

“They've raised their hand”
“They've raised their hands”

Does object have to agree with subject? To make the question more clear, let's assume all of them have raised their right hand/hands(?). Now we have five people and five raised hands.

I've changed the original question which used idiom "to show one's true colors" as example, which was giving the idea that my question was about usage of the specified idiom. I apologize for my poor choice of example.

  • It sounds like a pirate convention, if they show black flags ;) colours means flag. If they would be showing hands, you can use the singular if each of them shows one hand: five people raised their hand, although their hands would not be wrong — but hands might mean each person raised both their hands. – oerkelens Feb 11 '15 at 7:42
  • You need to give a more descriptive example. In "Five people are showing black color.", I have no idea what black color really is. Also you should edit the title to follow your example, and remove "They've shown their true colors" as is causes confusion with the idiomatic expression as you already noted. – user3169 Feb 11 '15 at 8:15
  • @user3169 I've edited the question. Is it any better now? – Sandeep D Feb 11 '15 at 8:30
  • The question now avoids one interesting idiom, but I'm afraid it now is a duplicate. This question has been asked in several shapes and forms... The question I linked to uses hands in the answer. – oerkelens Feb 11 '15 at 8:56
  • Changing a question so considerably that given answers become completely and totally unrelated may lead to confusion, by the way. I will remove my answer because it has nothing to do with the question as it stands now. – oerkelens Feb 11 '15 at 8:59

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