g–r colour radial profile at six different heights above and below the NGC 4565 mid-plane up to 4 kpc but excluding the mid-plane. Solid pink lines are the profiles from the disk region affected by a warp (north quadrant) while the green ones indicate the profiles of the region of the disk with no warp feature (west quadrant). The vertical shaded pink area highlights the warp region. The colour profiles show two moving U-shape features, characteristic of a star formation threshold. The first U-shape is at the truncation radius and close to the mid-plane, while the second traces the warp beyond R ∼ 38 kpc and above 1.5 kpc in height.