Add colours to right hand facets

ggplot_RH_colour_facet.R

# this adds colours to the right hand facets
colour_right_facets <- function(plot){
  g <- ggplot_gtable(ggplot_build(plot))
  stripr <- which(grepl('strip-r', g$layout$name))
  fills <- c("grey90","grey70","grey50")
  k <- 1
  for (i in stripr) {
    j <- which(grepl('rect', g$grobs[[i]]$grobs[[1]]$childrenOrder))
    g$grobs[[i]]$grobs[[1]]$children[[j]]$gp$fill <- fills[k]
    k <- k+1
  }
  grid.arrange(g)
}