How to assign colors to specific raster values using R

Question

I am using the levelplot function of the awesome rasterVis package to create a map whose values diverge around zero. I am plotting a raster file using a red to blue palette, but I am trying to assign grey to zero values in the map.

Specifically, I want to reproduce the colors of this figure:

Notice that where a red to blue scale is used, but zero values have been colored with grey.

Currently, my maps looks like this:

And this is the code to reproduce it (file available at https://www.dropbox.com/s/cypfdu1eaz2fuok/r.annual.tif?dl=0):

# Load required packages
library(rasterVis)

# open file
r.annual <- raster("Downloads/r.annual.tif")

# Set color palette
myTheme=rasterTheme(region=brewer.pal('RdBu', n=11))

# Plot
levelplot(annual.mask, par.settings=myTheme, margin=F)

How can I assign grey to all zero values in my map above?

Answer 1

You can define your own color palette by concatenating two predefined color palettes and your desired gray color as: [red orange yellow palette] + [zero gray color] + [blues palette]. To get zero value aligned with the gray color you have to use the same number of colors (n) for the predefined color palettes.

Try the commented code below:

# Load libraries
library('rasterVis')

# open raster file
r.annual <- raster("r.annual.tif")

# Set color palette
zeroCol <-"#B3B3B3" # (gray color, same as your figure example)
reds <- rev(brewer.pal('YlOrRd', n = 7))
blues <- brewer.pal('Blues', n = 7)

myTheme <- rasterTheme(region = c(reds, zeroCol, blues))

# Plot
levelplot(r.annual, par.settings = myTheme, margin = FALSE, main = expression("Precipitation" ~ (mm ~ year^{-1})))

Notice that your plot won't look like the figure example you posted because your raster have more sparse data with many Nas