Colour is Weird (Part 2)

Let’s up the ante on colour weirdness another notch. Under the right circumstances it is possible to see impossible colours – to directly experience the visual appearance of colours that, not only do not exist in nature, but physically cannot exist. Here’s how. First, recall from Part 1 that the LMS response curves overlap. Even when viewing pure Red (mostly in the L range) it isn’t possible to prevent the M or S cones from also responding a little bit – no matter how bright or pure the red source you are looking at. Ah, but what if there were some way to shut off those other cones? You’d see a vivid red that you’ve never experienced before because it cannot possibly be observed in the real world.

So, the trick is to stare at something long enough to physically exhaust those cones. And then look away. It’s a bit like the old optical illusion of staring at a colour image for a while and then looking away to a white page – you see an afterimage in reversed colours. Well, let’s experience it on steroids. Look at the red ball in the image below (an excerpt from Skytopia’s Eclipse of Titan - go see the whole site if you want to experience even more). Never mind about the blue-green square on the right. Just stare at the red ball. In particular, stare at the single white pixel in the centre of the ball (get up close if necessary). And stare at it for a long time. Not the lame 15-30 seconds done for most optical illusions. I mean a long time. At least 2 full minutes. And when you are done, quickly look away. You will see an afterimage of course. But it will be in shades of blue and green that you have never seen before! They are impossible colours that cannot exist in nature anywhere (as proof of this, notice that you cannot find them anywhere in the square on the right, containing all the blues and greens possible on your screen). Try it now:

This technique is causing the L cones to get so fatigued that they temporarily switch off. When you then turn your eyes away from the red ball, you get to experience what it is like to see the world with zero L response. You see colours comprising only M and S responses. The brain has never had to make sense of that set of optical inputs before (completely lacking an L response). There is nothing you can look at in the world that directly has this colour. It exists only in your mind. Weird?

 Colour and Art

And now you are in a position to have some insight into a controversial painting in the National Gallery of Canada, Barnett Newman’s The Voice of Fire. It’s quite large, but it’s just three stripes of colour, two blue, one red. Any child could have painted it. But if you ever visit the gallery, a sympathetic security guard might tip you of to the correct way to view it. Like with the Eclipse of Titan, you must stare at it a long time. And then quickly look away. When you look away you will briefly be able to see an afterimage drawn in “impossible” colours – stripes of impossibly flaming orange! That’s the voice of fire. Not the painting. The painting is just an instrument or tool to prepare your eyes to see the real artwork, which exists only in your mind!

How about a weirdly reversed case? What happens if you give the brain too many inputs, instead of too few? To achieve this, we would need to feed the brain a combination of LMS responses that normally would be impossible to see together, such as completely complementary colours (e.g., Blue and Yellow) at the same time. Consider the image below. It is a “crossed-eye stereo pair”, meaning that you are meant to look at it in a peculiar way. Cross your eyes while looking at it. Try to get the + on the blue square to precisely line up with the + on the yellow square (you might need to adjust your head position a bit). You will know you have it right when it looks like there are three squares in the image: on the left a blue one, on the right a yellow one, and in the middle… a weird one. What colour is that middle square, anyway? It is certainly not green (blue + yellow). Colours add in a way very unlike how the brain added binaural sounds. Weird.

Incidentally, this crossed-eye technique is commonly used to view 3D images such as the below photo of an Aeolian harp I once made. To see it, cross your eyes in the similar fashion (aligning the picture frames with each other) so that you see three framed pictures. You will be able to look through the middle frame, to where the harp can be seen in full 3D.  

Good thing I kept this stereo picture. I installed this harp in the middle of a patch of poison ivy, in a forest clearing, off the beaten path, in a remote corner of the Rouge Valley. And yet someone has stolen it already. Sigh.