normalize <- function(x) {
  r = range(x)
  m = r[2] - r[1]
  (x - r[1]) / m
}

colors = rainbow(8)

p1 = xyplot(Sepal.Length~Sepal.Width|Species,iris,col=colors[round(normalize(iris$Petal.Length)*7)+1])

p2 = xyplot(Sepal.Length~Sepal.Width,iris,col=colors[round(normalize(iris$Petal.Length)*7)+1],pch=as.numeric(iris$Species))

print(c(p1, p2))