If #SPVoid didn't have Crimson right eye, his eyes would be black voids, but that's not the only reason why he wanted that eye...

Each one of the forsaken Lords was given a gift of Mayhem, that they could use with Soledormir power, but with it was also a curse.
Given each one this power Soledormir branded his chosen champions with a mark, the forsaken are also unable to kill one another without their masters consent.

Rage (his mark is on his left shoulder)
Could cause eruptions in the Earth and lava flows.
(He can still split the ground and cause earthquakes)

Malice (his mark is on his chest)
Could raise the Dead with anything his Darkness corrupted, this including his dark fog.
(He can still corrupt and control, if he foce and use enough for his Magic it might be possible for him to be able to bring one back to life....)

Demise (her Mark is on her right wrist)
(Has not been revealed yet)
She has an fast recovery and can't be kill useless if her bracelet is removed.

Void (his mark is on his left eye)
(Has not been revealed yet)
He is the only one of the forsaken who can still use his gift fully with out Soledormir being released, and it's the reason how he knows so much.
( And no it's not mind reading that's to OP )

Omen is not one of the Forsaken, he is also able and has kill Forsaken Lord in the past with out Soledormir giving him permission.