Chapman's Piloting (57 edition, 1985 printing, original printing 1917) states and I quote...
"The use of color coding for racing and cruising sailboats is common. The lines may have a solid color, or be white with a colorer 'tracer'. A recomended stardard is:
Mainsail, sheet and halyard- white
Jib/Genoa- blue,
Toping lifts-green
Vangs and travelers-orange"
So coming clean, I would have to say that Chappy is a tradition and by virtue of its contents, I would also suggest that the standard he recommends is therby also a tradition. So weak as my argument may be, I cite Chappy as my witness that the tradition, albeit young is indeed what I would call ... a tradition.
I have also seen many starborad and port lines color coded green and red, and some (my own original lines inclueded) had green and red whippings on the appropriate jib sheets.