Why do I get the same output with the two following statements plot3d(0, 0..20, 0..70, color=proc(x,y) 200000*x end proc); plot3d(0, 0..20, 0..70, color=proc(x,y) x end proc); How does the option "color=proc() ..end;" works? How can I choose the colors? (The reason behind my question is that I am trying understand how to plot the Mandelbrot set)