15.64.40  OUTLINE 

This  enables  the outline on each axis.  The outline is the line drawn at
the edge of the plot.
SET {OUTLINE|FRAME} [INHIBIT|ENABLE] [ALL|TOP|BOTTOM|RIGHT|LEFT] [ON|OFF]
     [INTENSITY|WIDTH=n]
     [NOCOLOR|WHITE|RED|GREEN|BLUE|YELLOW|MAGENTA|CYAN]
     [NOTEXTURE|SOLID|DOTS|DASHES|DAASHES|DOTDASH|PATTERNED|FUNNY|SPACE]
     [PERMANENT]
This acts on the current plot only if PERMANENT not specified.  To control
other individual elements of the axes use:
SET AXES, SET TICKS, SET LABELS, SET SCALES

(Default:ON)