Does yellow stop a Green Lantern ring?
In Hal Jordan’s Silver Age stories, the ring could not affect a yellow object directly. His first issue, Showcase #22 (1959), presents him with a yellow missile and makes him find a way around the restriction. Read Showcase #22.
Green Lantern: Rebirth (2004–05) gives the old rule a new explanation. In that telling, a Lantern can overcome the impurity by recognizing their fear and using willpower to push through it. DC’s history timeline (story spoilers).
The Sinestro Corps deliberately channels fear through yellow rings, which is a different use of the color. DC’s Sinestro profile (story spoilers).