15.64.43  PEN 

This selects the default Calcomp plotter  pens  or  the  color.   This  is
effective only for the current plot, or until another SET COLOR or SET PEN
command.
     SET PEN 1|2|3|4|5|6|7

See:Command SET COLOR

(Default:1)

If no pen number is specified it is set to 1.