Change ggplot2 colourbar tick marks to black

Question

In some of my plots I find it hard to see the tick marks in the colour bar. I haven\'t been able to find a documented way to change the colour of the ticks. All the examples

Answer 1

The pull request mentioned in another answer never made it into the ggplot2 code base, but this is now possible in a slightly different way in the development version (slated to be released as ggplot2 2.3):

ggplot(df, aes(x, y, fill = val)) +
  geom_raster() +
  scale_fill_gradient(low = "#FFFFFF", high = "#de2d26") +
  guides(fill = guide_colourbar(barheight = unit( 3 , "in" ),
                                ticks.colour = "black",
                                ticks.linewidth = 1)) +
  theme_bw() +
  theme(line = element_line(colour = "#0000FF"))

You can also add a frame, which may be useful when some of the colors in the colorbar are very light.

ggplot(df, aes(x, y, fill = val)) +
  geom_raster() +
  scale_fill_gradient(low = "#FFFFFF", high = "#de2d26") +
  guides(fill = guide_colourbar(barheight = unit( 3 , "in" ),
                                ticks.colour = "black",
                                ticks.linewidth = 1,
                                frame.colour = "black",
                                frame.linewidth = 1)) +
  theme_bw() +
  theme(line = element_line(colour = "#0000FF"))

Answer 2

EDIT: Please refer to the answer below by Claus Wilke.

---

I have included the original answer below, but please note that it is now outdated and I do not recommend using it.

I included the functionality to customize tick marks and legend borders in my fork of ggplot2. I have submitted a pull request, but thought I would let people know here in case they stumble on this question.

Install my fork using the following code,

if (!require(devtools))
  install.packages('devtools')
install_github('paleo13/ggplot2')

We can specify black marks using the following code,

ggplot(df, aes( x, y, fill = val)) +
  geom_raster() +
  scale_fill_gradient(low = "#FFFFFF", high = "#de2d26") +
  theme_bw() +
  theme(line = element_line(colour = "#0000FF")) +
  guides(fill = guide_colourbar(barheight = unit(3, "in"),
   ticks=element_line(color='black'), border=element_line(color='black')))

(I would have included this as a comment but I lack the reputation to do so, if anyone with sufficient privileges wants to delete this answer and move the contents to the comments then feel free)

Answer 3

I usually find what I need to change by extensive use of str. I'm sure others can do it more elegantly.

g <- ggplotGrob(p)
g$grobs[[8]][[1]][[1]]$grobs[[5]]$gp$col <- "black"

library(grid)
grid.draw(g)