Metal wire was invented in approximately 400 AD.  Barbed wire was invented in the 1870’s.  Plaintiff began selling barbed wire in 1889.  It began coloring the top wire strand red in 1920 (and received a trademark registration for red top wire fencing in 1921).  Its KING RANCH wire is pictured above.  Defendants began selling green top wire fencing in 2000.  Plaintiff obtained a preliminary injunction as it has “a better than neglible chance” of establishing that defendants’ placement of any color (not just red) on the top wire of a barb wire fence will likely cause confusion with plaintiff’s mark.  Keystone Consolidated v. Midstates Distributing, 65 USPQD2d 1492 (CD Ill Dec 2002) (decision applarently not online).

More on the history of barbed wire here.