If they are on your screen, champion healthbars should never disappear unless they die

There are particle effects and sounds flying everywhere during a teamfight. Some champs have abilities that make them untargetable, and when that happens their healthbar disappears sometimes. The confusion tends to come from when they are almost dead. Healthbar disappears and everyone thinks they're dead. Their support thinks they've died and so does the enemy.

This happens with Elise and Yi because their body disappears. It's more obvious with Elise but during a teamfight it's harder to see Yi.

It does not happen to Vladimir.

I think the issue disappeared with Fizz due to the invulnerability bar change, but it used to happen to him too.

Can we get a color around the healthbar (like red or something) that indicates untargetability?