Scale data on a plot by opacity?

Hi,

I have a set of data that is plotted, in 2D, as a bunch of points (a scatter plot). Each point also has an intensity associated with it. How can I plot the data such that the intensity is represented by relative opacity of one shade of color?

I.e. currently I'm specifying the appearance of the points with 'ro' string, such that each point is a red dot. How do I change this to be scaled such that the most "intense" value is deep red, and the least intense values are grey-red? The key is not to vary color, but to vary opacity in one color.

I've seen this done before, so I know it's possible.

Thanks!

[Star Strider]

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