r - Out of bound colour scale plot in raster

Question

I have a raster and I want to plot it using image(). So far, I plotted the raster with my own color scale col.

## read the libraries
library(raster)
library(fields)
library(grDevices)


##random raster object
set.seed(1)
r <- raster(ncol=5, nrow=5)
r[] <- rnorm(n=ncell(r),mean=2)

col = colorRampPalette(c("darkred","red","lightskyblue","blue","blue4"))(20)
image(r, xaxs="i", yaxs="i", col= rev(col))

This looks like

.

Now, I want to plot the all the values higher than the value 2 as "darkred" (initial color from my color scale)

I found a similar post and tried the same

zlim=2
newcol = ifelse(raster(r) >= zlim,"darkred",col)
image(r, xaxs="i", yaxs="i", col= newcol)

However, I got some error message. It would be helpful if anyone can help me with this.