Minecraft: 1.12.2
Forge: 14.23.5.2824

Mods: 5
AoV-1.12-0.11.4
Forgelin-1.7.4
leveluphp-1.12.2-1.4.0
ShadowMC-1.12-3.8.0
TamModized-1.12.2-0.15.6

The Red Bar under the Green XP Bar is the Health XP.

Top Image:
Spell Bar is rendered and for some reason the Health XP bar from the mod "Level Up HP" is transparent to where you almost can't see it.

Middle Image:
The Spell Bar is lit up while attempting to select a spell and the Health XP bar lights up as well.

Bottom Image:
If you have any spell equipped in the slots, the Health XP HUD bar remains lit up.

Not shown:
If a spell icon is red it causes the Health XP Bar to render a darker red than usual.