specify breaks in divergent palette in RColorBrewer: was divergent colors around zero in levelplot()

Bert or anyone else familiar with RColorBrewer:

Has anyone tried to accomplish with RColorBrewer what I asked about in my original post (below)? 

Here is an example cribbed from the levelplot() help examples

x <- seq(pi/4, 5 * pi, length.out = 100)
y <- seq(pi/4, 5 * pi, length.out = 100)
r <- as.vector(sqrt(outer(x^2, y^2, "+")))
grid <- expand.grid(x=x, y=y)
grid$z <- cos(r^2) * exp(-r/(pi^3))

# now use RColorBrewer to get a palette

library("RColorBrewer?)
levelplot(z~x*y, grid,col.regions=brewer.pal(6,"BrBG?))   # the numeric argument to brewer.pal is the number of colors used ? I tried several

This gives me a nice brown-to-green gradient but does not (AFAICS) give me control over where the center of the divergence lies. Even in this symmetrical
example, I can?t get it to be at zero ? it repeats on either side of zero.

thanks to anyone who pages through all this and makes a suggestion, even if it doesn?t work.  :-)

Use the Rcolorbrewer package.

-- Bert

On Fri, Nov 22, 2013 at 8:43 PM, Don McKenzie <dmck at u.washington.edu> wrote:

I would like to produce a levelplot with divergent colors such that increasingly negative values of Z get darker in the first color and increasingly
positive values get darker in the second color.  this is common in cartography. I have tried tinkering with the col.regions argument but the best I can do
is to get the split in the middle of my range of Z, but in my particular case range(Z) is (-1,12).

I am using R 3.0.2 on OSX 10.9

Here is an example

x <- y <- c(1:25)
grid <- expand.grid(x=x,y=y)
grid$z <- sort(runif(625,min=-1,max=12))
levelplot(z ~ x*y,grid)   # produces the default pink and blue but the split is at ~5.5

# do something clever here
# e.g., my.colors <- <create a palette that splits at zero>

levelplot(z ~ x*y,grid,col.regions=my.colors)  # so there should be some light pink at the bottom and the rest increasingly intense blue

Ideas appreciated.  Thanks in advance.

Bert Gunter
Genentech Nonclinical Biostatistics

(650) 467-7374

Don McKenzie
Research Ecologist
Pacific Wildland Fire Science Lab
US Forest Service

Affiliate Professor
School of Environmental and Forest Sciences
University of Washington
dmck at uw.edu