What does it mean if in a dream I am bitten by a blue and red snake but it's a dry bite and then I kill the snake?

It means you had a dream. Congratulations. Dreams don't necessarily have meaning, in fact you shouldn't even try to interpret it. It's not an exact science. It's closer to an art form you're assuming all the meaning of to be factual or set in stone.

Hey, wait... Maybe you're afraid of snakes?