Change the color of a ggplot geom a posteriori (after having specified another color)

Question

A function from a package returns a ggplot with preset colours that I'd like to change.

For example, let's simulate that plot:

library(ggplot2)
df <- data.frame(x = rnorm(1000))

p <- ggplot(df, aes(x=x)) +
  geom_density(fill="#2196F3")
p

It is a blue-filled density plot.

I'd like to change its color a posteriori.

I've tried doing:

p + scale_fill_manual(values=c("#4CAF50"))
p

But it doesn't change anything.

I've also tried:

p <- p + geom_density(fill="black")
p

But that adds a layer on top of the previous one, without changing it.

I've also attempted to dig into the ggplot object but I got lost there.

Is there any convenient way to change the properties of a geom a posteriori?

Thanks

Answer 1

Try this:

#this is blue
p <- ggplot(df, aes(x=x)) +
  geom_density(fill="#2196F3")

#convert to red
p$layers[[1]]$aes_params$fill <-  'red'
p

The fill colour is saved in p$layers[[1]]$aes_params$fill and can be modified this way.