‘You’re not going out dressed like that!’

Who doesn’t remember that moment? An irate parent at the foot of the stairs, challenging our right to wear what we like.

Rainbows, lines or wheels? Art, religion or science? Humans have wondered what colour is and how it works since the first rainbow appeared in the sky.

‘They do it with mirrors!’

Magicians famously swear an oath never to reveal the secrets of their tricks. In colour analysis, I work with mirrors too.

My stomach lurches as I walk into the Garden Room in this smart Berkshire hotel. The sun’s in my eyes, patterning brilliant squares across the top of a vast table piled with manuals. Four faces look back at me.