This command sets the line colour for the data set <ik>. If <ik> is 0 the colour set is taken for the grid lines (-> grid "on" | "off"). The colours are numbered like the pens on a HP7475 plotter. Allowed values for <c> are:
1 : red 4 : purple 2 : green 5 : yellow 3 : blue 6 : black