Question with multiple 3d plot colors

[Patufet P]

Hello,

I would like to know how several surfaces on the same graph could be
shown with the color corresponding to the height Z.
With a single surface this works great:

f=scf();
f.color_map=jetcolormap(256);
t=[0:0.3:2*%pi]';
z=sin(t)*cos(t');
plot3d(t,t,z)
e=gce();
e.color_flag=1;

but if I add different surfaces afterwards

plot3d(t,t,z+5)
e=gce();
e.color_flag=1;

the colors are mapped for each new surface.

What I would like is that one color corresponds to one height for all
the graphs.

Thank you for any hints.

Regards.