When equipped, it caused your own text in chat to appear black, even if it appeared gray to other players due to being infected with The Gray Plague.
References
The fact that it only makes your own text look better, whilst it remains the same to other players, is probably a reference to the phrase "Seeing the world through rose-tinted glasses." This phrase means that one is only looking at the pleasant side of things, and ignoring the unpleasant.
