How to obtain ideal color scale in corrplot?

Question

I have a matrix that I am trying to visualize using the corrplot package in R. The values in this matrix are fold changes of a treatment group relative to a control group (1 meaning there is no change, >1 meaning treatment group enhanced, <1 meaning treatment group reduced). Is there a way to utilize corrplot such that all values < 1 are on a red gradient, all values > 1 are on a green gradient, and all values = 1 are white?

Here is what I have tried:

Sample data:

testdata = matrix(rnorm(10, 1, 0.1), nrow = 5)
testdata
          [,1]      [,2]
[1,] 1.1368602 1.0123854
[2,] 0.9774229 1.0215942
[3,] 1.1516471 1.0379639
[4,] 0.8451247 0.9497677
[5,] 1.0584614 0.9666793

corrplot(testdata, is.corr = FALSE, col.lim = c(0, max(testdata)))

That produces the following:

As you can see, there is no demarcation between values > 1 vs < 1. If anyone is able to share any way to set a transition point on the corrplot package that places all values > threshhold as being on one color gradient and all values < threshhold as being on another color gradient I would be extremely grateful! Thank you for your time.

EDIT: Additionally, the values in the matrix range from 0 to >3 but I am still hoping to keep the 'white' transition point of the color legend of the corrplot at 1. If I use the suggestions from the helpful answers below it only works if the range of values in the matrix is between 0 and 2 which sets white transition point of color legend at value of 1. A range of 0 and 3, for example, sets the white transition point at 1.5 whereas I would like it to remain at 1

Answer 1

You could do that with col argument.

library(corrplot)
#> corrplot 0.92 loaded

set.seed(123)
testdata = matrix(rnorm(10, 1, 0.1), nrow = 5)
corrplot(testdata, 
         is.corr = FALSE, 
         col.lim = c(min(testdata), max(testdata)),
         col = COL2("RdBu"),
         )

^{Created on 2023-05-03 with reprex v2.0.2}

Edit
You can manually control gradient range with ggcorrplot. Note that ggcorrplot can be compatible with ggplot2, thus you can use scale_fill_gradient2().

library(ggcorrplot)
set.seed(1234)
testdata = matrix(runif(10, min=0, max=3),nrow=5)
ggcorrplot(testdata) +
  scale_fill_gradient2(limit = c(0,3), low = "red", high =  "blue", mid = "white", midpoint = 1)
#> Scale for fill is already present.
#> Adding another scale for fill, which will replace the existing scale.

^{Created on 2023-05-03 with reprex v2.0.2}

Answer 2

I'm not aware if you can use uneven divergent scales. But for an even divergent, with minimum as 0, like you stated and the scale centered on 1 you could do this:

corrplot(testdata, is.corr = FALSE, col = COL2('RdBu', 10), col.lim = c(0, 2))