What colour is this?  What about this?  And this?  Or this?  Assuming you’re not colour blind, I’m hoping the answers to those questions were red, blue, green and yellow respectively.  But what is colour?  In scientific terms, it’s how we perceive light of varying frequencies being reflected off objects.  Some objects reflect light of higher frequencies than other objects, hence they reflect different colours, and appear coloured differently.

But is blue, blue?  Or red, red?  As in, what’s to say our eyes don’t see colours as they should.  Do we see the same blue as someone else?  The trouble is that it’s difficult to know.  We can’t exactly perceive the world through someone else’s eyes.  What one person sees as a certain colour, may been seen completely differently by someone else.

We already know about colour blindness, in which people have a limited subset of available colours to them, and so see other colours as those within their range (for example, someone who could only see red and yellow would see blue as more of a red, and green as more of a yellow).  We also know that some animals, such as dogs, only see in black and white.  But what if there are other differences in perception?

Hue spectrum
A basic hue spectrum.

Take a look at the chart above.  Thinking just about the range of colours (ignoring saturation and luminosity), everything must be coloured by one of the colours in the spectrum.  So now here’s one idea: what if one person sees the world like another person, but with the hue shifted?

Hue spectrum, shifted
The lower spectrum has been shifted to the right.

As in, say that one person saw red.  Then another person might see pink instead.  If one sees green, the other sees yellow, and so on.  Doesn’t sound too bad, does it?  Well, let’s try it on a photo.

Hue-shifted photo
As you’ve probably guessed, the hue’s been shifted on the right.

Well, that certainly doesn’t look right!  It’s like it just turned from summer to autumn.  Shame you can’t keep going and get to winter.  Also, pink faces?  Just…  no.  So the question is, does this actually happen?  Quite possibly.  Although, if someone’s vision was like that on the right, wouldn’t they know that they’re seeing the world in all the wrong colours?  Well…  no.

Think about it.  You’ve been brought up your whole life being told that red is red, and blue is blue.  Regardless of what colour you’re seeing, you’ve been told what it is.  It doesn’t matter what colour it was originally perceived as when it was first named, nor does it matter what the name is.  However you see the world, you will have seen it like that forever, and so will probably be convinced that your perception is the ‘right’ one.