A photo of the space would really help generate useable advice. ”Vestibule” sounds to me like a closed off separate space than, say, a ”foyer”. If it is, it could be treated as a separate space. But, it is a nice thing to have the colors in a home flow from one room to the next - to connect the spaces. Will you have any green in the decor of the rooms / spaces immediately outside the vestibule? And, is there any natural light in the vestibule? The answer to that might affect the shade of green that would look best.