One key factor is luminance, or the amount of light a color reflects. A green background has a much higher luminosity than a blue one, making a green screen a better choice for daytime scenes when you want your shots to look bright and well lit. But a blue screen can be handy in scenes where you don’t need so much light.
“If you’re trying to composite around an actor in a night scene, you want to go with a blue screen,” Yeager recommends. “It’s darker, so it’ll reflect less light back on them, which means less color spill to deal with in post-production. Color spill is when the color of the chroma key background is reflected back onto the actor. This can make the keying process more difficult, so you want to avoid color spill as much as you can.”
Costumes and hair color
If the scene you’re shooting absolutely requires a character to wear green, you should use a blue background, and vice versa. But even colors that don’t match the background can still cause a problem. “Blond hair can be difficult to key out on a green screen because of the way light reflects through it. It’s almost a little bit translucent and you get color spill,” Yeager says. “A blue screen gives you a much stronger contrast with blond.”