使用python画图怎么设置渐变色

from turtle import *

setup(500, 400, 200, 200)

penup()

fd(-250)

pendown()

pensize(20)

seth(-40)

r = 0.1

g = 0.2

b = 0.3

for i in range(4):

    pencolor((r+0.1*i, g+0.1*i, b+0.1*i))

    circle(40, 80)

    circle(-40, 80)

pencolor((r+0.1*4, g+0.1*4, b+0.1*4))

circle(40, 80/2)

fd(40)

pencolor((r+0.1*5, g+0.1*5, b+0.1*5))

circle(16, 180)

fd(40*2/3)

done()