How to plot curves with more than 8 colors

Hi,

I'm a new hand in R language. I have about 20 groups of data[x,y] and
want to plot them on a graph. To do this, I write a for-loop as
following: (some codes are omitted for simplicity)

for (i in c(1:20))
{
  points(...,...,col=i)
  lines(...,col=i)
}

The problem is "R only plot them with 8 colors repeatly". Could anyone
help me solve this problem? Or is there any package providing plot
function without color limit?

Best Regards...