I will jump
will indicates future
This is called Dramatic Irony. The definition of this is in the question.
Bradbury repeatedly uses the color gray to describe the parlor. He chooses this color to show the depressing nature of the parlor. He sees the viewing parlor as a way for people to turn off from experiencing life and the world around them. All the vibrancy of life is drained out.
In contrast when he talks about the park he uses the color green. Green symbolizes life, growth, vitality. He's showing that society has become dull and miserable inside their homes instead of alive and joyous in the world.
