1) Filmmakers use lighting and color filters to manipulate the mood and tone of a scene. The temperature of light (cool blue/green vs. warm pink/gold) and use of shadows, spotlights, and backlighting can set a romantic, ominous, or revealing atmosphere.
2) Color is the norm for films but some directors choose black and white to emulate older genres or highlight important moments with selective color.
3) Modern digital tools allow extensive post-production manipulation of color, but natural lighting techniques are also used to dramatic effect.