R Plotly 3D: Add Mesh to Scatter plot without inheriting color scheme

Basically I have a scatter 3d Scatter plot with the points in two categories (selected, unselected) which are represented in red and grey. To better visualize the selected volume I want to add a cube with low opacity in blue. However, when I add the mesh for the cube, the cube appears in green and the unselected points in orange instead of grey.

In short: Why is the cube not blue and the unselected points not grey and how can I make them do so?

library(shiny)
library(plotly)


ui <- fluidPage(
  tags$h2("This is my 3D plot."),
  plotlyOutput("Plot3d", width = "1000px", height = "1000px")
)

server <- function(input, output, session){
  output$Plot3d <- renderPlotly ({

    #Defining data frame for scatter
    df_scatter <- data.frame(X_VAL = rnorm(50, mean = 0.5, sd = 0.15),
                             Y_VAL = rnorm(50, mean = 0.5, sd = 0.15),
                             Z_VAL = rnorm(50, mean = 0.5, sd = 0.15),
                             SCATTER_COL = rep("unselected", 50))
    
    #Every point inside of the cube is labeled "selected" 
    for (i in 1:nrow(df_scatter)){

      if (df_scatter$X_VAL[i] < 0.5 && df_scatter$Y_VAL[i] < 0.5 && df_scatter$Z_VAL[i]< 0.5) {
        df_scatter$SCATTER_COL[i] <- "selected"
      }
    }
    df_scatter$SCATTER_COL <- factor(df_scatter$SCATTER_COL, levels = c("selected", "unselected"))
    
    
    #Defining data frame for mesh
    df_mesh <- data.frame(X_VAL = c(0, 0, 0.5, 0.5, 0, 0, 0.5, 0.5),
                          Y_VAL = c(0, 0.5, 0.5, 0, 0, 0.5, 0.5, 0),
                          Z_VAL = c(0, 0, 0, 0, 0.5, 0.5, 0.5, 0.5),
                          MESH_COL = factor(rep("CUBE", 8), levels = c("CUBE")))
    
    
    
    plot_ly()%>%
      add_markers(type = "scatter3d", 
                  mode = "markers", 
                  data = df_scatter, 
                  x = ~X_VAL, 
                  y = ~Y_VAL, 
                  z = ~Z_VAL, 
                  color = ~SCATTER_COL, 
                  colors = c('red', 'grey')) %>%
      
      #Here the trouble starts
      add_trace(type = 'mesh3d',
               data = df_mesh,
               x = ~X_VAL,
               y = ~Y_VAL,
               z = ~Z_VAL,
               i = c(7, 0, 0, 0, 4, 4, 6, 1, 4, 0, 3, 6),
               j = c(3, 4, 1, 2, 5, 6, 5, 2, 0, 1, 6, 3),
               k = c(0, 7, 2, 3, 6, 7, 1, 6, 5, 5, 7, 2),
               color = ~MESH_COL,
               colors = c("blue"),
               inherit = FALSE,
               opacity = 0.1
      )
  })  
}
shinyApp(ui = ui, server=server)

Any help is greatly appreciated.

Solution

Try facecolor:

library(shiny)
library(plotly)
#> Loading required package: ggplot2
#> 
#> Attaching package: 'plotly'
#> The following object is masked from 'package:ggplot2':
#> 
#>     last_plot
#> The following object is masked from 'package:stats':
#> 
#>     filter
#> The following object is masked from 'package:graphics':
#> 
#>     layout

mycolors <- colours()[2:10]
ui <- fluidPage(
    tags$h2("This is my 3D plot."),
    plotlyOutput("Plot3d", width = "1000px", height = "1000px")
)

server <- function(input, output, session){
    output$Plot3d <- renderPlotly ({
        
        #Defining data frame for scatter
        df_scatter <- data.frame(X_VAL = rnorm(50, mean = 0.5, sd = 0.15),
                                 Y_VAL = rnorm(50, mean = 0.5, sd = 0.15),
                                 Z_VAL = rnorm(50, mean = 0.5, sd = 0.15),
                                 SCATTER_COL = rep("unselected", 50))
        
        #Every point inside of the cube is labeled "selected" 
        for (i in 1:nrow(df_scatter)){
            
            if (df_scatter$X_VAL[i] < 0.5 && df_scatter$Y_VAL[i] < 0.5 && df_scatter$Z_VAL[i]< 0.5) {
                df_scatter$SCATTER_COL[i] <- "selected"
            }
        }
        df_scatter$SCATTER_COL <- factor(df_scatter$SCATTER_COL, levels = c("selected", "unselected"))
        
        
        #Defining data frame for mesh
        df_mesh <- data.frame(X_VAL = c(0, 0, 0.5, 0.5, 0, 0, 0.5, 0.5),
                              Y_VAL = c(0, 0.5, 0.5, 0, 0, 0.5, 0.5, 0),
                              Z_VAL = c(0, 0, 0, 0, 0.5, 0.5, 0.5, 0.5))
        
        plot_ly()%>%
            add_markers(type = "scatter3d", 
                        mode = "markers", 
                        data = df_scatter, 
                        x = ~X_VAL, 
                        y = ~Y_VAL, 
                        z = ~Z_VAL, 
                        color = ~SCATTER_COL, 
                        colors = c('red', 'grey')) %>%
            add_trace(type = 'mesh3d',
                      data = df_mesh,
                      x = ~X_VAL,
                      y = ~Y_VAL,
                      z = ~Z_VAL,
                      i = c(7, 0, 0, 0, 4, 4, 6, 1, 4, 0, 3, 6),
                      j = c(3, 4, 1, 2, 5, 6, 5, 2, 0, 1, 6, 3),
                      k = c(0, 7, 2, 3, 6, 7, 1, 6, 5, 5, 7, 2),
                      facecolor = rep("blue", 12),
                      opacity = 0.1
            )
    })  
}
shinyApp(ui = ui, server=server)

^{Created on 2020-07-02 by the reprex package (v0.3.0)}