How to make points one color when a third column equals zero, and another color otherwise, in Gnuplot?

Question

I need to vary the point color for a row of values based on the color in one column. The data:

# x y z
1, 3, 0  
1, 5, 6  
3, 5, 2  
4, 5, 0

<

Answer 1

You can adjust the palette by

set palette defined (-0.1 "blue", 0 "red", 0.1 "blue")