Hi Matiroh,
It seems you are trying to draw plane at specified z with color determined by linear interpolation from the upper and bottom plane. Something like:
Mat(3) = (Mat(2)-Mat(1))*(z-z1)/(z2-z1)
But if you need the graph to be updated automatically with input z, that will need some coding. Please email us <tech@originlab.com> with more details and your serial number, we can help you further.
James