turtle渐变填充

import turtle

pen = turtle.Turtle()
pen.speed(0)
pen.colormode(255)
l = 200
r = 255
g = 2
b =50
for j in range(50):
    pen.fillcolor(r,g,b)
    pen.begin_fill()
    for i in range(3):
        pen.forward(l)
        pen.rt(120)
    pen.rt(20)
    pen.end_fill()
    l = l-2
    r = r-3
    g = g -2
    b = b +4