The blue-eyed finger is a stock character played by Peanut. He is one of the first characters to be played by Peanut. He is presumed to be a boy, because Inka said "Hello sir" to him at the pool, in his only appearence Swim to the Brim!. He has no lines, and one of his only actions is when he, for some reason, took the swim diaper Inka made Oobi, Charlie, and Dave wear.
So far it is unknown what the blue-eyed finger looks like, but he is a finger and is most likely small and a peach color.
He only made one appearence in Swim to the Brim!.