[R] How to alpha entire plot?

[Ed Siefker]

I have two chromatograms I want plotted on the same axes.
I would like the plots to be transparent, so the first chart is
not obscured.

I have tried adjustcolor(..., alpha.f=0.3), the problem is that
my chromatogram is so dense with datapoints that they
overlap and the entire graph just ends up a solid color.  The
second histogram still obscures the first.

Consider this example:


col1 <- adjustcolor("red", alpha.f=0.3)
col2 <- adjustcolor("blue", alpha.f=0.3)
EU <- data.frame(EuStockMarkets)
with(EU, plot(DAX, CAC, col=col2, type="h", ylim=c(0,6000)))
par(new=TRUE)
with(EU, plot(DAX, FTSE, col=col1, type="h", ylim=c(0,6000)))

The density of the red plot around 2000 completely obscures the blue
plot behind it.

What I would like to do is plot both plots in solid colors, then alpha
the entire thing, and then overlay them.  Or some other method that
achieves a comparable result.
Thanks