A) Evolution is not directed. If a pre-tiger happens to be a more advantageous colour, it will have more offspring. There is no goal.

B) An orange tiger has the same camouflage from its prey’s point of view as a green one, which is the thing that really matters. There is only one species a tiger is afraid of, and it’s humans. I would wager that the orange also happens to act as a signal colour, both to other tigers and other predators (such as humans). Less run-ins and less territorial dispute sound pretty good.