What is your interpretation of the colored light at the end of The Giver?
My interpretation of this is that it is Christmas time and the lights are Christmas lights.
This makes sense for a number of reasons. First, it is clearly winter because there is plenty of snow on the ground. Second, the lights are of appropriate colors and the book says that the lights are twinkling on trees. That makes it pretty clear that it is Christmas time. Finally, the end of the book is clearly based on the memory that the Giver gives Jonas earlier in the book. In that memory, it was Christmas as well.
So I think it's pretty clear that the colored lights are Christmas lights.
I think that the colored lights and their meaning are dependent on what has happened to Jonas. I agree that they are Christmas lights, because Jonas' experience has entailed Christmas lights.
Since one interpretation of the ending of the book has been that Jonas and Gabriel die, it would stand to reason that his memories would be of the good memories that the giver had shared with him. Christmas is one of the special memories.
Another thought is that the lights are that of a city up ahead. Jonas has never seen a city that would be different from his home. If he is on a hill and coming downward he would see street lights and house lights in different colors.