Specify the range of color range of marker_z

I am using Plots.jl to plot 3-D in 2-D colormap using:

scatter(x, y, marker_z=z, color=:jet)

The color is automatically map to range [zmin, zmax] of the vector z. However, to compare several cases (of z), I hope to fix the colorbar to represent the range of [z1, z2] and independent of the z vector.

Thank you.