Chromatlas

Idea

Is your red my red?

When you and I both say “red”, do we see the same thing? Philosophers have argued about it since 1690.

Inverted spectrum
John Locke, 1690
Mary's room
Frank Jackson, 1982

Qualia (singular quale) are the felt qualities of experience: the redness of red as it looks to you. Here's the puzzle. You and a friend both call a tomato red and grass green. What if the way red looks to you is the way green looks to your friend, and the reverse? You'd use every color word identically, so no naming test could ever reveal it.

John Locke posed this 'inverted spectrum' in 1690, in his Essay Concerning Human Understanding, imagining a violet giving one person the same idea a marigold gives another. He thought it wouldn't make anyone's ideas false, since both would still sort the world the same way. Philosophers have used the case ever since to ask whether experience is fully captured by behavior and brain function.

Color science pushes back a little. Color space isn't symmetrical: pure yellow is far lighter than pure blue, and some regions hold more distinguishable shades than others. A simple swap of red and green might show up in odd judgments, like which color looks lighter or more like a sunset. An inversion clever enough to keep every relation intact remains, for now, untestable.

Two more thought experiments sharpen the question. Frank Jackson's 1982 'Mary' is a scientist who knows every physical fact about color vision but has lived all her life in a black-and-white room. When she first sees a red tomato, does she learn something new? And Ludwig Wittgenstein, in his Remarks on Colour, asked what color words can mean at all. Meanwhile color blindness shows people really can see differently, and prove it.

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