In The Giver, color is symbolic of the larger idea of emotions. When Jonas develops the Capacity to See Beyond, it opens a window of memories for him. With those memories come emotions.
Jonas first sees color when he notices something strange about the apple that he is throwing to Asher. There is an emotional connection between Jonas and the apple. He sees red when he is helping his friend, but he does not know it. He even risks punishment by taking the apple home to inspect it further. Jonas has seen his first glance of a large world, but it only confuses him.
There was absolutely nothing remarkable about that apple. … And again—in the air, for an instant only—it had changed. (ch 3, p. 24).
The incident with the apple is the first time Jonas realizes that he is different from others. When he is singled out at the Ceremony of Twelve, he is humiliated at first. Then he realizes he has been given a great honor. He understands that he deserves it, because he sees the faces change. He sees the pink tones of their skin, and realizes he does have the Capacity to See Beyond.
But when he looked out across the crowd, the sea of faces, the thing happened again. The thing that had happened with the apple. (ch 9, p. 64)
Thus the colors are the thing that first gets Jonas his job as Receiver of Memory, and therefore they are what give him access to the memories. Jonas begins to see color because he has those memories. He feels emotions for the first time.
Jonas asks The Giver why the people no longer have colors. He is highly interested in the colors.
Jonas wasn't interested, just then, in wisdom. It was the colors that fascinated him. "Why can't everyone see them? Why did colors disappear?" (ch 12, p. 95)
The community, when moving to Sameness, wanted to eliminate emotions. Emotions make people weak. They make them uncomfortable. They cause conflict. All of these things need to be eliminated in the community. This is why Jonas is different. He can see the color, and he can feel the emotions. He understands what it means to feel.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.
Jonas first starts to understand color by chapter 12 in Lowry's novel The Giver. After describing his experiences with the apple and with Fiona's hair, the Giver realizes that Jonas is discovering the hues of color; so, he gives him the memories of the sled and the hill of snow and of a rainbow so Jonas can really start to learn about joyful memories. Jonas comes back the next day really upset that colors were one of the things/memories sacrificed to maintain peace in his community. In fact, he angrily says, "It's not fair" that society can't see color (97). The Giver asks him to explain, to which he answers, "If everything's the same, then there aren't any choices! I want to wake up in the morning anddecide things! A blue tunic, or a red one?(97). At this point the Giver and Jonas discuss the fact that colors provide opportunities for preference and choice. Without anything specific to choose, then there wouldn't be any disappointment if or when the choice didn't come to the intended result. Disappoint is a type of stress or pain; therefore, it was elliminated along with the colors. Hence, the answer to the question above is that Jonas realizes that through the lack of colors in life, he also lacks the freedom to make choices.