how do you know if your colourblind or if someone else is? – my blue could be your yellow.

Question: how do you know if your colourblind or if someone else is? - my blue could be your yellow.
- Keywords:
  blue,
  colour,
  yellow
Asked by rubyfernfern to Charlie, Eoin, Jemma, Julian, Steve on 19 Mar 2011.
- Jemma Ransom answered on 18 Mar 2011:
  
  That’s a fantastic question!
  
  It’s perfectly possible that what I would call blue looks very different from what you call blue, so how do we tell if someone is colourblind?
  
  My boss has red/green colour blindness, and the way we can tell this is if we show him a picture involving red and green, he can’t tell the difference between the two colours where we can. So I think it is the distinguishing between colours that is missing in colour blindness.
- Eoin Lettice answered on 18 Mar 2011:
  
  There are special colour blindness tests that you can take and they’ll show if you’re colour blind or not. Your optician will have these or there are some charts here too.
  http://colorvisiontesting.com/online%20test.htm
  
  Eoin
- Julian Rayner answered on 18 Mar 2011:
  
  Hi rubyfernfern. Wow, great question. Steve, being the blindness expert, can probably give you the best answer. However, the bigger question you are asking is one that fascinates me – how do I know that what I am seeing is real, and the same as everyone else is seeing? This is a question that has fascinated philosophers for a long time.
  
  A famous philosopher called Descartes, for example, started from exactly that premise – my senses are sometimes wrong, and I can’t trust them, so how do I know that the world exists? Then he started to try to prove that the world existed using pure logic, starting with the famous phrase “I think, therefore I am” – meaning that although he couldn’t know whether the world was real, he did know that he was thinking about the world, so he must exist somewhere as some sort of thinking thing.
  
  Sorry, we have wandered off science into philosophy, which I am no expert in at all, but I find that particular question really fascinating!
- Stephen Moss answered on 19 Mar 2011:
  
  Hi Rubyfernfern
  
  You probably wouldn’t realise you were colourblind until someone says something that makes you realise that two objects that you think are the same colour, are not. For example, you might be playing pool and your opponent sets the balls up and says to you, can you pass me the green. You have a group of balls next to you but they all appear red. That’s when you would realise for the first time that you’re red-green colourblind.
  
  But your other question is one that continues to puzzle – when I see yellow, am I seeing the same colour that you see when you see yellow? We can never be 100% certain, but we think we do see colours the same because we all have the same set of pigments in our retinas that detect the different colours. And the wiring from those cells to our brain is the same in all of us.
- Charlie Ryan answered on 19 Mar 2011:
  
  this sounds like a great question, but im really dont know anything about coloublindness! i’m curous to see what the answer is though! Stephen??

Question: how do you know if your colourblind or if someone else is? - my blue could be your yellow.

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