[R-sig-Geo] specifying different colors for vector map as background

[Jaime Carrera]

Hi,
I'm trying to create a spplot with a vector map on the background. It 
works fine if I don't want the polygon map to be filled, but what I do 
want to is to have the polygons filled with different colors. The 
following command plots the polygon map fine, filling each polygon with 
its respective color:

plot(avi,axes=FALSE,lty=0,col=rgb(avi$r/255,avi$g/255,avi$b/255))

Now I try to do this on ssplot, but it doesn't work, as all polygons are 
filled with the first color found:

basemap<-list("sp.polygons",avi,fill=rgb(avi$r/255,avi$g/255,avi$b/255),lty=1)
spplot(wells2001sp,c("May","Jun"),as.table=TRUE,sp.layout=list(basemap))

Is there a way around it?

Thanks,

Jaime