Per-channel scale override fails with Plot.raster

[Fil]

This should show the high-vapor-value pixels in red.

Plot.plot({
  color: {scheme: "blues", legend: true},
  x: {transform: (x) => x - 180},
  y: {transform: (y) => 90 - y},
  marks: [
    Plot.raster(await vapor(), {
      width: 360,
      height: 180
    }),
    Plot.raster(await vapor(), {
      width: 360,
      height: 180,
      fill: {value: (d) => (d > 4 ? "red" : null), scale: null}
    })
  ]
});