A colored surface

To add colors to the surface you need to pass color data to the plot command.
As in this example, you can just reuse the z value. Alternatively you could
pass some independend color data. ...

To bring colors instead of black/white to the surface, you need to change the
gradient. Be sure to use the same color space for the gridcolor and the
backcolor too.

! In this example we also modified the projector. By that you can change the
view angle, and you can also (as in this example) use a parallel projection
instead of the default central projection. While the later looks more natural,
a parallel projection keeps lines parallel independend from their depths. An
very simple justification of the parallel projection is the vertical z axis,
which stays vertical in the projection. Also the linear axes have equal
distances between the ticks, which is not true for central projections.

! Skipping the value for the z component will allow you to plot this surface
on a two-dimensional graph as well.
