In R, is there a way to color plot points on a gradient based on a range of numbers?

Question

I'm new to R, and I've been able to plot points, but wondering if there is a way to apply a color gradient to the scatterplot.

I have a 3 column matrix, where the first two will be used as coordinates, and the third has range of numbers between 0 and .0001. Is there a way to color the plot points based on where they fall in the range of numbers?

 x   y   z
 15  3   6e-4
 34  22  1e-10
 24  1   5e-2
 ...

plot(x, y, main= "Title", ylab = "column y", xlab = "column x", col = rgb(0,100,0,50,maxColorValue=255), pch=16) 

Answer 1

I'm big on the ggplot2 package, because it does a lot to encourage good plotting habits (although the syntax is a bit confusing at first):

require(ggplot2)
df <- data.frame(x=x, y=y, z=z) #ggplot2 only likes to deal with data frames
ggplot2(df, aes(x=x, y=y, colour=z) + #create the 'base layer' of the plot
  geom_point() + #represent the data with points
  scale_colour_gradient(low="black", high="green") + #you have lots of options for color mapping
  scale_x_continuous("column x") + #you can use scale_... to modify the scale in lots of other ways
  scale_y_continuous("column y") +
  ggtitle("Title") 

Answer 2

How about

plot(x, y, col = gray(z/0.0001)) 

This is by gray.