Your Blue is my Green

On John Locke, Crayons, and the Case for Epistemic Humility

Some nights, when I’m putting my five-year-old daughter to bed, she’ll protest that her room is too dark.

That declaration kicks off a kind of practised routine between us. I begin listing the light sources; a soft cloud light at the far end of the room, a kitty nightlight on the adjacent wall and before I can stop myself (even though I can already sense the intellectual dead-end I’m walking into), I reply: “No, your room is not too dark.”

The matter settled, or at least declared so, she rolls over, unconvinced. Her experience has been denied, and mine defended.

I’ve come to realise these little moments aren’t about the lighting. They’re about something much more complex: whose perception gets to count? What do we do when someone, especially a child, tells us about their sensory world and it doesn’t match our own?

That question, hiding in bedtime routines and dinner table disputes, is at the heart of one of philosophy’s oldest puzzles: how do we know what we know — and can we ever be sure someone else sees the same world we do?

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This tension is best represented by colour shift theory: the idea that our perception of colour isn’t fixed or universal, but influenced by our biology, our brain, and even the context in which we see it. One person’s “red” might be slightly shifted for someone else, and we’d never know. It’s both a perceptual question and a philosophical one: if our senses don’t align, can we ever truly share an experience?

John Locke, the 17th-century philosopher famously divided the world into primary and secondary qualities. Primary qualities — like mass, shape, and motion — exist independently of any observer. But secondary qualities — colour, sound, taste, temperature — are different. They don’t belong to the object itself, but arise in the interaction between the object and the perceiver.

“The ideas of primary qualities resemble their causes; those of secondary qualities do not.”

In other words, your child might not just be imagining a different red (or a darker dark) — they might be genuinely experiencing one. And you can’t prove otherwise. Children don’t need a philosophy degree to arrive at Locke’s conclusion. If anything, they have a natural gift for perspective-shifting; an ease with the idea that someone else’s reality might be different from their own.

It’s much harder for adults to recapture that flexibility of mind. That’s why philosophy courses so often begin with that very quest: how do we know what we know? This question belongs to a branch of philosophy called epistemology — the study of knowledge itself: what it is, how we acquire it, and how we know it's true. The difference is that children get there not by reading Locke, they just need curiosity and a box of crayons.

Adults deserve our sympathy though. There's a good reason to calcify one’s beliefs over time — it frees us up to expend energy elsewhere. Given the amount that is expected of a modern parent, is it really surprising that we’re not all still drifting around, slack-jawed, staring up at the sky, wondering, "is my blue the same as your blue?"

This insight is more than a parlour trick of the mind. It has real implications for how we parent. Because if colour lives in the mind, then so does everything else shaped by sensation — brightness, loudness, temperature, flavour. And if, as Locke believed, children arrive in the world as tabula rasa — blank slates — then everything they know must be written through direct experience. That doesn’t just call for patience; it calls for what philosophers call epistemic humility: the willingness to acknowledge that someone else’s experience of the world might be valid, even when it doesn’t match our own.

And how often, as parents, do we argue — quite uselessly — about these secondary qualities? "This soup isn't salty.", "That music isn’t loud.", "The water isn’t cold."

We argue as if perception is a court case to be settled, rather than a lens to be honoured. As if we haven’t been taught — by our kids, and by Locke — that the mind plays an equal role in shaping what we call reality.

Brain Development and the Subjective World

Neuroscience strongly supports this view. A child’s brain is still learning to categorise colours. Their cones are active, their vocabularies expanding, their neural circuits pruning and re-growing. What they see today may literally not be what they’ll see tomorrow. In that sense, colour isn’t just subjective — it’s developmental. Can we not extend that idea to other qualities of their perception?

For neurodivergent children, this fluidity can be even more pronounced. A child with sensory sensitivities may quite literally experience the world more intensely: brighter lights, sharper sounds, more saturated colours. When they say “it’s too scratchy,” they’re not exaggerating — they’re reporting.

To a parent, a practical response — “Come on, that shirt isn’t scratchy, we’ll be late” — might seem benign. But for the child, it can land differently: a quiet invalidation of their experience. Another time they’re asked, however gently, to set aside what feels true in their body in favour of someone else’s version of reality. These moments accumulate, not out of cruelty, but out of mismatch, and regrettably they shape how a child learns to speak up, or stay quiet.

A More Compassionate Lens

So how do we implement these ideas without slipping into the extremes of soft parenting — where children are always right, and their opinions take precedence over a household’s values and boundaries?

The answer lies in distinguishing validation from capitulation. Honouring a child’s perception doesn’t mean surrendering authority or structure. It means acknowledging their experience as real even when the response must still be a firm no. You can say, “I believe you that the shirt feels scratchy,” and still follow it with, “but we do need to wear something warm today.”

It’s not about letting kids run the show. It’s about modeling what respect looks like in the presence of disagreement. When children feel that their inner world is seen, even when their requests are denied, they don’t just learn to self-regulate. They learn that their voice matters, and that others’ voices do too.

Closing the Distance

So when your child next says something like “it’s too dark,” or asks a question about colour, or sound, or anything else on the soft edges of perception — don’t rush to correct them. Sit with them in their reality. Entertain buying a third nightlight. Tell them about Locke.

Maybe their blue really is our green. And maybe that’s the beginning of bridged understanding — not the end.