Darken or lighten colors in R

darken.R

darken <- function(color, factor=1.4){
    col <- col2rgb(color)
    col <- col/factor
    col <- rgb(t(col), maxColorValue=255)
    col
}


lighten <- function(color, factor=1.4){
    col <- col2rgb(color)
    col <- col*factor
    col <- rgb(t(col), maxColorValue=255)
    col
}

# Example:
darkFirebrick <- darken("firebrick")

Thanks!
For lighten() the following appeared more natural to me. Larger factors make color more light with a factor of 1 generating white:

lighten <- function(color, factor = 0.5) {
  if ((factor > 1) | (factor < 0)) stop("factor needs to be within [0,1]")
  col <- col2rgb(color)
  col <- col + (255 - col)*factor
  col <- rgb(t(col), maxColorValue=255)
  col
}