Creation of 2D-color gradation plots

[c-wohlers]

Hello,

I would like to create a 2D color gradation plot. In the PyX-examples is the density plot, so somethinig like this. But data points are not evenly distributed. Thus this plot type does not work.
In examples about 3D-plots is the colored surface and in the text you describe: "Skipping the value for the z component will allow you to plot this surface on a two-dimensional graph as well." But I am not able to do this.
Can you please give an example an how to plot a colored surface in a 2D-graph?

Thankyou

[c-wohlers]

In the FAQ I also found the section "How can I plot grid data?":
But the mentioned examples are no longer existing