Yellow Plague 01

In a possible future, Guy Gardner succumbs to the disease.

Quote1 Can't breathe -- >GASP< I've turned all yellow! Quote2
--Guy Gardner

The Yellow Plague of Ghera is a mysterious and deadly illness with no known cure. It proves fatal to adults, and is especially feared by and deadly to members of the Green Lantern Corps. In the possible future where he is picked as the world's first Green Lantern, Guy Gardner is killed by the plague. On a journey to the planet Ghera, he finds it has decimated every adult on the planet and left only the children, immortal, who occupy their time with dangerous war games.[1]

It has also been explained that the yellow plague is responsible for killing off half of Green Lantern Varix's homeworld Naktos, including his predecessor Ghrelk.[2]