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"))