How to setup the background color on a radial plot?

Question

I need to draw a target. I have selected the plotrix library. My current result and code are below:

library(plotrix)

pmax  <- 30 

rho   <- seq(pmax, 7.5, by=-2.5) 
phi   <- seq(0, 360, length=10) 

radial.plot(rho, phi, rp.type = "s", point.symbols=19, 
           radial.labels=seq(pmax, 10, by=-5), start=pi/2, clockwise=TRUE, labels=LETTERS[1:4], main="Test Radial Plot")

Question. Is it possible to fill all circles of the target with different colors in plotrix library? Or should I use alternative library?