Running through this whole thread, Gl1tch's "simulation" idea seems the wisest. Instead of kludging together a bunch of random qualifiers on what makes the yellow bar a certain size, why not just simulate the end of your opponent's next turn and give that outcome in yellow/red?
That said, I can see a reason to have an exception or two - in the case of Bone Wall/Phase Shield, having yellow displayed (without any opposing momentum) will let you know how quickly you'll be damaged after the shield expires.
It's not like the vets really need it fixed, the main reason I see for fixing the yellow bit is to avoid feeding newbies confusing information. "The bar wasn't all yellow! Why did I die?" "Were you being attacked by something with adrenaline?" Far better PR from Zanz's standpoint to have as few information-barriers as possible between a new player and enjoying the game.