How is the inability to see color a symbol for the lives of the people in Jonas's community? How is it important with regards to theme and...

Color represents emotion, and the community controls it because it wants to keep people in a diminished state.

No one in Jonas’s community can see colors except the Receiver of Memory.  It may seem like a simple thing, until you realize how closely color is connected to our emotions.  Do you have a favorite color, or a color you prefer to wear?  This is an expression of your individuality.  It gives you choices, and makes them clear to others around you.

Jonas starts seeing colors before he is even chosen Receiver of Memory.  He does not know what this means at first.  He sees the color red in an apple, and flesh tones in the faces of the crowd.  When he explains to The Giver that he noticed Fiona’s hair, the old man tells him he is seeing color.

The concept of color opens up a whole new world for Jonas.  He realizes that with color comes choice.  Choice is restricted for the community in almost every way.  He starts to understand that the absence of color is another example of this restriction.

"Well ... "Jonas had to stop and think it through. "If everything's the same, then there aren't any choices! I want to wake up in the morning and decide things! A blue tunic, or a red one?" (Ch. 13) 

The absence of color was a deliberate choice, in addition to eliminating sunshine, hills, most animals, and a whole host of social choices.  People do not choose their spouses or occupations, and they do not have their own biological children.  Emotion is absent from every aspect of their existence. 

The community wants to prevent people from feeling, because feeling might lead to uncomfortable feelings.  Love is wonderful, but what if your heart gets broken?  It’s better to just eliminate it.  You get the side benefit of controlling the population.

Through his training, Jonas realizes how wrong Sameness is.  Everything he took for granted seems twisted.  He notices that if he stops taking his pill for Stirrings, his emotions come back.  No one else has them.  The minute people approach adolescence and mature thought, they are stunted.