define a virtual palette with the minimum allowable cube size
PALvirt MinCube
{
vclass = VIS_CLASS_PSEUDO;
share = SHARE_CMAP;
cube_size = 2;
};
MinCube defines a virtual palette that uses a pseudo-color, shareable visual with the minimum cube size of 2. This subclass is useful if you are going to configure one or more Datamaps to be used directly as ramps. Using the minimum cube size leaves the most amount of space open in the colormap for use by ramps.