This pull request closes issue #3072.

The issue has been fixed by changing the number of colors generated by brewer_pal from 6 to 7. The mid-point now has a color that matches the mid-point on the color scale. This change was implemented in scale_color_distiller(). The function scale_fill_distiller() also had this issue and was also fixed.

library(ggplot2)

dat <- data.frame(x = -1:1)

ggplot(dat) + geom_point(aes(x = x, y = 1, color = x), size = 12) +
 scale_color_distiller(palette = 'RdBu', direction = 1, limits = c(-1, 1))

ggplot(dat) + geom_raster(aes(x = x, y = 1, fill = x)) +
  scale_fill_distiller(palette = 'RdBu', direction = 1, limits = c(-1, 1))

^{Created on 2019-01-19 by the reprex package (v0.2.1)}