They changed transparency apparently
Iris 1.4.2

Iris 1.4.3

I also encountered this problem, but in fact, if the color to be illuminated is pure, such as #00FFFF, you will not encounter this error.

I think it should be a problem with iris, but I haven't checked whether the glowing eyes of entities such as EnderMan are normal.

This must be the problem

IrisShaders/Iris@c695022

Doesn't happen anymore in recent versions.

What is your Iris version?
Can you create a small example project that shows this issue?

What is your Iris version? Can you create a small example project that shows this issue?

The iris Mod version I use is 1.6.6
CPM Model: https://github.com/FurryRbl/OpenAssets/blob/main/old/OC/Personal/Minecraft/SharpIceX/Model/CPM/SharpIce4.0.cpmmodel
CPM Model Project: https://github.com/FurryRbl/OpenAssets/blob/main/old/OC/Personal/Minecraft/SharpIceX/Model/CPM/SharpIce4.0.cpmproject

Doesn't happen anymore in recent versions.

The problem still seems to exist