Jonas and the other community members are unable to see color because the community has eliminated colors in an effort to maintain sameness.
Sameness is the community’s name for complete control over everyone’s lives. They want to ensure that everyone in the community shares the same experiences, as much as they can. For some reason, they have determined that color is dangerous. Although it is not entirely clear why color is gone, other than the fact that it differentiates things, and any kind of differentiation is bad in this world.
When Jonas first begins to see color, he asks the Giver why the colors are gone. Even he does not really seem to understand why. His answer is to shrug.
"Our people made that choice, the choice to go to Sameness. Before my time, before the previous time, back and back and back. We relinquished color when we relinquished sunshine and did away with differences." (Ch. 12)
Jonas is not even aware that colors exist, and that he does not have them, until he begins to see the color red when tossing an apple. The fact that he sees skin tones next indicates to us one reason why they might have eliminated color. It would seem to eliminate racism. They can’t even tell what color a person’s hair is. The fact that Jonas has light colored eyes they can tell, and it is a source of secret shame or embarrassment to them. Any difference is not to be tolerated.
Another reason for eliminating color is clear when Jonas begins discussing choices with The Giver. The seemingly innocent discussion of choosing choices of colored clothes comes up.
"But now that I can see colors, at least sometimes, I was just thinking: what if we could hold up things that were bright red, or bright yellow, and he could choose? Instead of the Sameness."
"He might make wrong choices." (Ch. 13)
So there is the issue. Even with the simplest matter of choosing what color clothing to wear, one might make the wrong choice. If we eliminate the ability to see color, color no longer matters, and there is no choice. Another choice is eliminated, and it becomes easier to have Sameness. As long as we have Sameness, the people are safe from all emotion. Peace reigns supreme.
As soon as Jonas begins to see color, he begins to question. In fact, it is the beginning of the unraveling of his world. He starts to notice that things are not what they seem. The perfect world is far from that. He learns about release, and finds out that the dark secrets are more than he can take, so he bolts. He cannot remain in a world that allows people no freedom.