Use of colour in plots

Here is an example doing the same type of thing. 
It should be easy enough to adapt. 

Good luck

===========================================================
x <- runif(100, 0, 1)
y <- runif(100, 0, 1)
z <- data.frame(x,y)

 plot(subset(z, z$y >=.5), col="red", ylim=c(min(z$y),
 max(z$y)), pch=16) 
 points(subset(z, z$y <=.49), col="blue", pch=16)
===========================================================

--- On Fri, 9/5/08, Steve Murray <smurray444 at hotmail.com> wrote:

From: Steve Murray <smurray444 at hotmail.com>
Subject: [R] Use of colour in plots
To: r-help at r-project.org
Received: Friday, September 5, 2008, 9:10 AM
Dear all,

I have 3 datasets all of which share the same longitude and
latitude values, which I'm looking to plot onto a
scattergraph. The third dataset has values which can only be
either '1' or '2'. So to incorporate all
three datasets onto two axes, I'm wondering if I can
plot dataset1 and dataset2 as normal, but then use colour to
determine whether these points are either values '1'
or '2' according to the third dataset.

If so, how would I go about doing this in R, and what
format would the command take?

Thanks for any help offered,

Steve