I think that their world is just basically a mirror of everything and everyone. I think this because Jonas was selected to be the receiver and he is experiencing color for the first time. It was his first time because their world is gray so he experienced red and the man that new that he was seeing red was the old receiver aka the giver. And he said “I experienced this in a different way a long long long time ago”. so that brings me to my next idea where the giver/receiver lives forever. I think this because when he said a long long long time ago he literally said long 3 times. And after he said they had color back then and since he is the giver he makes all the decisions for the community and he said it took he a long time figure out if we should have color again or not so he basically I think that he made the decision to get rid of color .