The outstanding characteristics that Jonas displayed, which led the Committee of Elders to select him to become the next Receiver of Memories, were his eyes and his perceptions of the world.
The irises of Jonas's eyes were light in color, which was very unusual in the community. The current Giver had light-colored eyes, as did his daughter - who had been named to become the next Receiver of Memories but asked to be released from the position. One younger child is also mentioned in the story as having light-colored eyes, but apparently everyone else has dark irises.
Jonas also has the gift to see beyond, to see things that the rest of the community is unable to see.
But when he looked out across the crowd, the sea of faces, the thing happened again. The thing that had happened with the apple. They changed. He blinked, and it was gone.
As part of the philosophy of Sameness that structures all life, the differences caused by color have been given up. Jonas, however, is able to recognize that objects have color and that different objects have different colors.
These abilities to see and experience beyond what the rest of the community could do made Jonas different in the midst of the sameness, and resulted in his being singled out for assignment as the next Receiver.