Morphological operation color

import cv2
import matplotlib.pyplot as plt
import numpy as np
def main():
    path = "C:\\Users\\edkni\\Downloads\\image_processing_files\\Dataset\\"
    imgpath = path + "4.2.03.tiff"
    img = cv2.imread(imgpath,1)
    img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
    
#    th = 0
#    max_value = 255    
#    ret,bin_inv = cv2.threshold(img,th,max_value,cv2.THRESH_BINARY_INV + cv2.THRESH_OTSU)
    
#    k = np.ones((5,5),np.float32)
#    k = cv2.getStructuringElement(cv2.MORPH_RECT,(5,5))
#    k = cv2.getStructuringElement(cv2.MORPH_ELLIPSE,(5,5))
    k = cv2.getStructuringElement(cv2.MORPH_CROSS,(5,5))
    print(k)
    #erosion is expanding of black in border
    erosion = cv2.erode(img,k,iterations = 3)
    #dilation is expanding of white from border
    dilation = cv2.dilate(img,k,iterations = 3)
    #gradient is erosion - dilation
    gradient = cv2.morphologyEx(img,cv2.MORPH_GRADIENT,k)
    outputs = [img,erosion,dilation,gradient]
    titles = ["original",'Erosion','Dilation','Gradient']
    for i in range(4):
        plt.subplot(2,2,i+1)
        plt.imshow(outputs[i])
        plt.title(titles[i])
        
    plt.show()
    
if __name__ == "__main__":
    main()