Adding border or background to scale legend guide_colorbar in ggplot2

Question

I have a colorbar within ggplot graph ranging from white to red and the white border is not very good visible on the white background.

Is there a way to color the tick marks in the legend differently or adding a border around the gradient scale?

Here is a minimal example:

df <- data.frame(x <- rnorm(10),
                 y <- rnorm(10),
                 fill <- rnorm(10))

ggplot(df, aes(x, y, fill = fill)) + 
  geom_point() + 
  scale_fill_gradient(low = 'white', high = 'red')

Answer 1

In the latest ggplot2 (development version, to be released as 2.3), this now works:

# devtools::install_github("tidyverse/ggplot2") # do this once
library(ggplot2)
df <- data.frame(x <- rnorm(10),
                 y <- rnorm(10),
                 fill <- rnorm(10))

ggplot(df, aes(x, y, fill = fill)) + 
  geom_point() + 
  scale_fill_gradient(low = 'white', high = 'red',
    guide = guide_colorbar(frame.colour = "black", ticks.colour = "black"))

Answer 2

Found a solution for my problem by using element_rect and fill argument.

df <- data.frame(x <- rnorm(10),
                 y <- rnorm(10),
                 fill <- rnorm(10))

ggplot(df, aes(x, y, fill = fill)) + 
  geom_point() + 
  scale_fill_gradient(low = 'white', high = 'red') + 
  theme(legend.background = element_rect(fill = "grey95"))

I would prefer a border just around the colorbar, but this seems not possible...