const ndvi = new RasterFunction({
  functionName: "NDVI",
  functionArguments: {
    visibleBandID: 3,  // Red band id
    infraredBandID: 4, // NIR band id
    scientificOutput: false
  }
});

const colormap = new RasterFunction({
  functionName: "Colormap",
  functionArguments: {
    colormapName: NDVI3,
    raster: ndvi
  }
});

layer.rasterFunction = colormap;