Re: Can't find colored jos, so...........
All this depends on what style you study. Within Seidokan Aikido Rod Kobayashi-sensei made a clear distinction between the ishizuki and kissaki of the jo. He even developed a third jogi where he explicitly designed the various movements with that idea in mind. I have been told that Tohei was adamant about the jo having a kissaki and ishizuki. Hence the two jogi have applications of strikes, thrusts, and "cuts" that would be consistent with one end having a hard, pointed metal ishizuki (the "back") while the "front" having a moderate, long, multi-edged and pointed steel blade. And if you've ever seen a real yari point you'd see what I'm talking about.
Let me also point out that some koryu arts were sogo bujutsu (comprehensive arts) and were not limited to just one or two types of training. Many had multiple aspects. And it was not unusual to have consistency in training among empty hand, sword, bojutsu, polearm, tanto, etc., etc., etc. Often you would learn something a certain way that seemed irrelevant ("but the jo doesn't have a tip or back side!") only to find that the idea was to transfer training from other aspects (yari work for instance). If you think of the vast number of skills that must be taught it makes vastly more sense to try to keep things consistent. It also reinforces core principles of the art across the weapons taught and is often indicative of a certain style.