I: a coloured band within each panel of a lattice bwplot

Hi all,
I would like to add to each panel of a bwplot a coloured central
band, centered on the mean of the values, being its width +- 2% of
the mean itself.

I know how to add lines, i.e. something like

bwplot(X ~ Y|FACTOR
       data=my.df,
       panel= function(x, y){
         panel.bwplot(x, y)
         panel.abline(v = mean(x, na.rm = T) - mean(x, na.rm = T) *
0.02 panel.abline(v = mean(x, na.rm = T) + mean(x, na.rm = T) * 0.02
})

but I cannot figure out how to shade the region included between the
two lines.

Generally speaking, you want to draw a polygon . There is no lattice 
wrapper for the 'grid.polygon' function, so you will have to use it 
directly. Check out

library(grid)
help(grid.polygon)

For this simpler case though, 'grid.rect' should be sufficient, e.g.

       panel= function(x, y){
           m <- mean(x, na.rm = T)
           grid.rect(x = unit(m, "native"),
                     w = unit(m * 0.04, "native"),
                     gp = gpar(fill = "lightgrey", col = "transparent"))
           panel.bwplot(x, y)
       }

Make sure to do a 'library(grid)' before this.

Deepayan