Unable to style colorbar in density mapbox

I am following the example given here: https://plotly.com/r/mapbox-density-heatmaps/

However, I am unable to change the color of the coloraxis (or use showscale = F or move the colorbar over on x).

The plot won't work unless coloraxis = 'coloraxis' is specified, and there doesn't seem to be a way to style the coloraxis.

# population density available from https://data.humdata.org/dataset/worldpop-population-density-for-haiti
pop_den <- read.csv(data_path)
plot_ly() %>% 
  add_trace(
    data = pop_den,  type = 'densitymapbox',  lat = ~Y,  lon = ~X,  z = ~Z,
    coloraxis = 'coloraxis',
    radius = 10) %>% 
  layout(
    mapbox = list(
      style = "carto-positron",
      zoom = 6.5,
      center = list(lon = -73.09, lat = 19.06),
      coloraxis = list(colorscale = "Grey", colorbar_x = 1.5)
      )
    )

まず、https://plotly.com/r/mapbox-density-heatmaps/ の R densitymapbox 例を issue のコードで再現し、coloraxis とその layout オプションがどのように処理されるかを調査します。coloraxis の色、colorbar の表示、colorbar の位置を、プロットを壊すことなく要求どおりにスタイル設定できれば完了です。