Seems trivial but how is that going to look when your HP is 109/126 ?
What about...
- no numbers on the portrait,
- an inner ring on the current character portrait that is distinctly colored and acts like a gauge,
- group portraits (left of screen) are round and are outlined by a similarly colored gauge,
- and a hot key toggle that displays/removes character HP above all party heads when you press it?
I find more annoying the perpetual glow on the actual character model.
This always bothers me too. I would rather see the HP like 29/20 if the character is already at full health. Maybe change the font color on the numbers to indicate that something special is effecting the current HP count (this coloring could apply to the ring gauge as well).