Changing colour of existing geom, with no grouping

Question

This is likely just a blunder from my side, not remembering how to do this. Non-the-less. Imagine a scenario where you have a function generating a ggplot. You give no grouping, and the points are all coloured black. For simplicity, imagine the plot below is the one returned.

library(ggplot2)
data(mtcars)
p <- ggplot(mtcars, aes(y = mpg, x = hp)) + 
      geom_point()

How would I now change the colour of the points in p, without modifying the function that generated the plot itself. Eg. changing the code to geom_point(col = "green") would not be the an option.

Answer 1

An easy way to do it is to add a dummy aesthetic mapping after the fact:

 p + aes(color = "forestgreen") + scale_color_identity(guide = guide_none())

A more permanent alternative, which is the equivalent of going back and writing the color = "forestgreen" parameter back into the geom_point call is:

p$layers[[1]]$aes_params <- list(colour = "forestgreen")