Z-Range for "colz" option of TH2D::Draw

when i use Draw(“colz”) for a 2-D histogram, the colour scale goes from 0 to the z_max by default. how do i change this range? ideally, i would want the colour scale to range between z_min and z_max.

The color scale with COLZ option goes from the mimimum of the histogram to the its maximum. Have you an example showing the problem you encountered ?