grid.rect(gp=gpar(col="gray")) levels <- round(seq(90, 10, length=25)) grays <- paste("gray", c(levels, rev(levels)), sep="") grid.circle(x=seq(0.1, 0.9, length=100), y=0.5 + 0.4*sin(seq(0, 2*pi, length=100)), r=abs(0.1*cos(seq(0, 2*pi, length=100))), gp=gpar(col=grays))