A file titled .gnuplot can be created in your home directory
(/home/username) with settings for Gnuplot to use at startup.
If you’re running on a non-Unix-like system (cough Windows), then this
file should be titled GNUPLOT.INI.
Gnuplot has 8 preset line types that it cycles through when generating graphs.
These 8 preset lines are made using colors that are shown to work well for
colorblind people.
If you regularly make plots with more than 8 lines, you may wish to define new
line types in the .gnuplot file.
An example .gnuplot file, based on the default but with two additional lines.
Line 9 is salmon-colored and line 10 is lightslategray.
set linetype 1 lc rgb "dark-violet" lw 2 pt 0
set linetype 2 lc rgb "sea-green" lw 2 pt 7
set linetype 3 lc rgb "cyan" lw 2 pt 6 pi -1
set linetype 4 lc rgb "dark-red" lw 2 pt 5 pi -1
set linetype 5 lc rgb "blue" lw 2 pt 8
set linetype 6 lc rgb "dark-orange" lw 2 pt 3
set linetype 7 lc rgb "black" lw 2 pt 11
set linetype 8 lc rgb "goldenrod" lw 2
set linetype 9 lc rgb "#FA8072" lw 4 pt 1
set linetype 10 lc rgb "#778899" lw 4 pt 1
set linetype cycle 10
The first 8 colors in the default (and this example) are set based upon colors that are readable for people with different types of color blindness. Some good articles on picking contrasting colors can be found on the somersault18:24 blog and on J*Fly.