Have you read the book "Lord of the Clans"? The red eyes in the "New" Horde have a different meaning:
It's still a sign that the orc voluntarily consumed demon blood. No doubt. But demon blood is like a super drug.
It makes you stronger, more bloodthirsty, and more ruthless. As Grom said, "You feel the strength of five!"
It was only after the Second War that these orcs were cut off from their influx of demonic energy, with the slaying of all warlocks within the Horde.
A merciless cold detoxification.
But where the orcs, who didn't have red eyes, eventually subsided, those with red eyes still have the feeling: they are, so to speak, on withdrawal every day. And they can't do anything about it.
(Apart from killing the demons to whom the blood belonged. Which Grom did at the end of the orc campaign and finally freed all the "red eyes" from their suffering)
And yet these orcs tend to be the ones with the most strength and willpower. THIS is the meaning of the red eyes in Thrall's Horde:
- Shame as they consumed demon blood and cursed themselves with it until the end of their lives.
- Respect as they battle their withdrawal every day and move on with their new orcish lives.
The red-eyed orcs were also the first to notice when the Legion launched their invasion in WC3. Remember the mission "Cry of the Warsong" where Hellscream said: "Don't you feel it Thrall? Just like in the old days! As if demons were near!"
He felt the rise of demonic energy in the world. Just thrown in like that.