why did jonas think that it wasn't fair that no one saw colors?

This is because colours are so beautiful. Jonas wanted there to be choices. The world that he knows was so stagnant and monochromatic. People needed to know beauty, pleasure and even pain.

Because Jonas liked the idea of "different" and to have choices in his life. Color added diversity to his life, and he wanted to share it with others.

Because they do not wont to be to treat someone bad because of the color.

Jonas wants everyone to see how beautiful colors are and that the world isn't black and white. He everyone to see how beautiful the Earth is.

He thought that color was a amazing thing that everyone should experience.

He thinks colors won't be a problem and that everyone should see them