You can use either green or blue. Green probably works best. The actors can not have anything green in their clothing. The cloth should be as pure green as you can get, and of a non reflective type. The cloth should be large enough that the actors can work at least three feet in front of the cloth. No wrinkles in the cloth. The cloth should be lit evenly and from the side in addition to the front light on the actors. This is to eliminate harsh shadows on the cloth.
Have fun.
Don