FR: add a root_color option for treemap traces

When using a colorscale on a treemap trace (without providing a root) the container is shown in black:

library(plotly)

labels = c("A1", "A2", "A3", "A4", "A5", "B1", "B2")
parents = c("", "A1", "A2", "A3", "A4", "", "B1")
values = c("11", "12", "13", "14", "15", "20", "30")

fig <- plot_ly(
  type="treemap",
  labels=labels,
  parents=parents,
  values=values,
  marker=list(colorscale='Reds'))

fig

Example taken from here: https://plotly.com/r/treemaps/

I'd like to change it to white.

In the python plotly library there is a root_color argument to do so:

fig.update_traces(root_color="lightgrey")

see: https://plotly.com/python/treemaps/

It would be great to have the same option in R.

Or is there any workaround to achive this?

Start with the R treemap example using labels, parents, values, and marker colorscale, then compare its behavior with Python's update_traces(root_color="lightgrey") example. The work is done when the R treemap API accepts an equivalent root color option and changes the color of the container without a supplied root.