Scale.color_none
Suppress a default color scale. Some statistics impose a default color scale. When no color scale is desired, explicitly including Scale.color_none will suppress this default.
Examples
xs = 1:10.
ys = 1:10.
zs = Float64[x^2*log(y) for x in xs, y in ys]
plot(x=xs, y=ys, z=zs, Geom.contour, Scale.color_none)