from PIL import Image
img = Image.new( 'RGB', (600,600), 'white' )
pixels = img.load()

for x in range(300):
   for y in range(300):
     pixels[x,y] = (255,0,0)

for x in range(300,600):
   for y in range(300):
     pixels[x,y] = (0,255,0)

for x in range(300):
   for y in range(300,600):
     pixels[x,y] = (0,0,255)

img.show()