Given a ggplot2 plot, matching colors on legend text with the keys

coloring_legend_text.R

library(grid)

# http://stackoverflow.com/questions/23588127/match-legend-text-color-in-geom-text-to-symbol
coloring_legend_text <- function(p){
    g <- ggplotGrob(p)
    names.grobs <- grid.ls(grid.force(g))$name 
    labels <- names.grobs[which(grepl("label", names.grobs))]

    # Get the colours
    # The colours are the same as the colours of the plotted points.
    # These are available in the ggplot build data.
    gt <- ggplot_build(p)
    colours <- unique(gt$data[[1]][, "colour"])

    # Edit the 'label' grobs - change their colours
    # Use the `editGrob` function
    for(i in seq_along(labels)) {
        g <- editGrob(grid.force(g), gPath(labels[i]), grep = TRUE,  
                      gp = gpar(col = colours[i]))
    }
    
    #Draw it
    grid.newpage()
    grid.draw(g)
    return(g)
}