Red-eye

Red-eye was originally thought to be a disease found amongst enslaved Ood on their homeworld of the Ood Sphere. Its symptoms were bright red eyes, rabid temperment and anti-Human sentiment.

It was caused by the subconscious of the Ood Brain reemerging amongst the Ood after 200 years of slavery, due mostly to the sabotage of Ood Operations's systems by the Friends of the Ood. It would later lead to the Battle of the Ood Sphere in 4126 and the freedom of the Ood. (DW: Planet of the Ood)

When the Ood used their new-found ability to see through time, their eyes glowed red once again. (DW: The End of Time)

When The Beast took over the Ood serving the Walker Expedition on Krop Tor in the year 43K2.1, they too experienced a Red-eye effect. (DW:The Impossible Planet/The Satan Pit)

It can be assumed from these instances that the "Red-eye" was not a sign of disease or malevolence amongst the Ood, but actually an indicator of an increase in their mental ability.