problems with overflow from yellow to white(python)

my task is this: having a white sheet, add text to it, embed a picture and make a gradient. I understood how to add text and embed an image. And here’s how to make an overflow. for example, from yellow to white or from black to white, I do not understand.I would also like to understand how to move a cloud The final picture should be like this.enter image description here

my code:

import cv2
white_list = cv2.imread('python_snippets/external_data/probe.jpg')
cloud = cv2.imread('python_snippets/external_data/weather_img/cloud.jpg')
white_list[:cloud.shape[0], :cloud.shape[1]] = cloud
org = (50, 50)
fontScale = 1
color = (255, 0, 0)
thickness = 2
cv2.putText(white_list, '+5', org, font,
                    fontScale, color, thickness, cv2.LINE_AA)
cv2.imshow('img', white_list)