Gnuplot supports two alternative sets of linetypes. The default set uses a
different color for each linetype, although it also allows you to draw dotted
or dashed lines in that color.  The alternative monochrome set uses only
dot/dash pattern or linewidth to distinguish linetypes. The set color
command selects the color linetypes.  See set monochrome (p. 
), set linetype (p. 
),
and set colorsequence (p. 
).