Green for the most part because when shooting digital, blue screen has a tone to it that human skin has as well so cropping becomes much more difficult. Even though our skin is tan the computer, when processing, doesn't know the difference that well and so cropping becomes more difficult. More so if you are poorly lit your set.

Even thought blue and green screen are both really close to each other, green screen would be the better choice over all.

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Imagination and discipline are like yin and yang; both are completely different and yet without each other they are nothing.