I posted this question as an issue to Gadfly.jl <https://github.com/dcjones/Gadfly.jl/issues/527>, and now realized that I have a better chance of getting an answer, if there is one, here.
I given some arrays xs, ys and zs that hold my data set, I can do plot(x=xs, y=ys, z=zs, Geom.contour) to get a contour plot of the data. On this plot, the contour lines are colored by the function value for each level. Is there a way I could, manually, color them all the same? // T