Colour is puzzling. Blue is particularly so. Colours are different to shapes because we seem to understand shapes without the need for prior experience of them. I doubt that any of us has ever seen a chiliagon. We wouldn’t be defeated by the challenge to imagine an object with 1,000 sides. Compare that to the plight of someone blind from birth asked to imagine that this chiliagon is blue. Unlike shape, we largely know of the world of colour through vision. If Hume was right about anything when he proposed that we can only have a simple idea if we have an impression or experience of it, we would think he would write about colour – colours like blue. But blue, surprisingly, might have been his undoing.

He asked us to imagine a sighted person who has been acquainted with all sorts of colours except some particular shade of blue. Looking through the paint tiles at the blues on offer, could this person register that this shade is missing? It would seem so. But how did our thinker get this idea of the missing shade? All we know about this shade is that it’s the one that hadn’t been seen. Maybe this is in the spirit of Emily Dickinson, who wrote:

The Brain is wider than the sky,
For, put them side by side,
The one the other will include
With ease, and you beside.

If she is suggesting that the mind’s contents can go beyond what we can take in passively through experience, I couldn’t agree more.

Part of what makes colour puzzling is that it seems that we both do and don’t need experience of them to think about them. Part of what makes colour puzzling is that it’s so very hard to locate. On a naïve view, colours are located on the surface of objects. It’s as if a thing’s colour is some impossibly thin skin or film stretched across its surface. The naïve view is hard to abandon but impossible to defend. Take the blue of the sky above; the sky and sea surely belong on our list of paradigmatic blue things. When we turn our gaze upwards, we can see why people thought the sky was a great dome (with a few holes to let light through giving us the appearance of stars). Were things this way, there would be nothing puzzling to mull over. But things aren’t this way. There’s no dome. There’s no object above that has a surface across which the colour might be stretched.

If we move towards where we think the blue should be, what we encounter is invisible and the blue retreats off into the distance. The blue is nowhere and yet we see it so plainly. Perhaps this is what Yves Klein meant when he said that blue was something that we can never touch or see but something inherently visible.

Science will tell us that we have the experience of blue because some wavelengths of light don’t reach us. Great. That doesn’t tell us whether we need to abandon the naïve picture. We’re left wondering whether to think of the sky’s colour as trouble for the idea that colours attach to objects or whether to embrace the view that a tile might be sky blue but that the sky could never be. It’s a funny thought that a tile that’s indiscernible from the sky might be the only sky blue thing we see, but maybe that’s right. Or maybe not. Seems like a pretty bad idea. We don’t need the mystical to worry about our grip on things. Blue is enough to cause trouble.

Clayton Littlejohn, Blue Revue, published by Blue Mountain School, 2018