It would be great if it was possible to make the health bar get darker together with the mobs, maybe make this a config option.

(If you use Hardcore Darkness it's even worse. -_-')

This is ages old omg. I will consider adding a config option for this for the newer versions

I managed to do it in a fork I made to backport some stuff to 1.7.10, see HostileNetworks@7c7e6cc

Not too difficult. The intermediate brightness levels could probably look better, but it's good enough for me (at light level 1 or 0 it is impossible to see). The health bar is still mostly visible when it's dim, but precise details (the text) are difficult to see. That's actually kind of immersive IMO.

Hopefully @Vazkii brings it into the latest for you guys not stuck on an old version like me :)