[R] Complex plotting problem

[Wee-Jin Goh]

Hello,

I would like to make a plot (preferably lines, but points will do  
too), where the line segment changes color depending on the value of  
the y-axis. For example, let's suppose the y-axis range is from -1 to  
1. Points close to -1 would be colored blue, while points close to 1  
will be colored red. Points in between will be varying degrees of  
blue/red depending on how close they are to -1 or +1.

If the above is not possible, would it be possible to set a decision  
boundary on the plot, where any point above this boundary will be a  
particular color, and any point below will be a different color?

Any suggestions as to how I might accomplish this would be much  
appreciated.

Regards,
Wee-Jin

p.s. The data set I'm talking about has about 20,000 points.