how_color() missing 1 required positional argument: 'color'

from images import Image

def posterize(image,rgb):
    whitePixel = (255,255,255)
    for y in range(image.getHeight()):
        for x in range(image.getWidth()):
            (nr, ng, nb) = image.getPixel(x,y)
            average = (nr + ng + nb)/3
            if average < 128:
                image.setPixel((x,y),rgb)
            else:
                image.setPixel((x,y),whitePixel)

def main():
    filename = input("Enter the image file name: ")
    red = int(input("Enter an integer [0..255] for red: "))
    green = int(input("Enter an integer [0..255] for green: "))
    blue = int(input("Enter an integer [0..255] for blue: "))                    
    image = Image(filename)
    posterize(image, (red, green, blue))
    image.draw()

if __name__ == "__main__":
   main()