I have the following line plot and want to fill the background using a color gradient relative to the monthly values of each year.
set.seed=500
dat <- data.frame("year"= c(2000:2005),"value" = c(1000,800,200,600,1000,900),"Jan"=runif(6,-3,3),"Feb"=runif(6,-3,3),"Mar"=runif(6,-3,3),"Apr"=runif(6,-3,3),"May"=runif(6,-3,3),"Jun"=runif(6,-3,3),"Jul"=runif(6,-3,3),"Aug"=runif(6,-3,3),"Sep"=runif(6,-3,3),"Oct"=runif(6,-3,3),"Nov"=runif(6,-3,3),"Dec"=runif(6,-3,3))
plot(x=dat$year, y=dat$value, type="b")