Reading Melmoth’s thought of the day of avatars that lose color as they lose health (instead of having health bars), I wondered what alternative option would be available for colorblind players. Systems that work poorly for the colorblind are shockingly common in video games, despite the perception of a male-majority playerbase and the prevalence of at least red-green colorblindness in men. I suppose that relatively few artists and graphic designers are colorblind, so concerns about the visuals surface later in the process.
An alternative would be having characters fade away as they run low on health. Set avatar opacity to their hit point percentage. This fits the lore of a potential game by postulating that the characters are more like einherjar than living beings, which makes more sense than most lore anyway: we are immortal warriors who train ourselves for the great battle at the end, dying daily but arising to continue the fight. In this case, the characters are souls who fade away as their connection to the mortal coil is severed. Characters become increasingly wispy as their connection to the world becomes tenuous.
This would have the effect of making healing much harder at low health, as you just stopped seeing people. Did Bob move or is he dead? This is especially so if you take away tab-based targeting. I like the potential effects of this combined with healing as an area-effect ability, so you would see fading souls frantically flocking to the aura of a spirit healer. It feels like a classic image of the hungry or hopeful dead.
This would also create the interesting PvP option of intentionally running around at low health. Will you accept the risk of being one-shot for near-invisibility?