Apple skin has a feature of showing potential health restored while holding food. When in hardcore this breaks and shows normal hearts instead of the hardcore hearts when colorful hearts is enabled.

Minecraft: 1.20.4
NeoForge: 20.4.200
AppleSkin: 1.20.4-2.5.1
Colorful Hearts: 1.20.4-7.0.2

squeek502/AppleSkin#291

Sorry about that. I have noticed the issue a few days ago but completely forgot about it. It should work fine now.