import turtle
t = turtle.Turtle()
ts = turtle.Screen()
t.speed(0)

ts.bgcolor("black")
r,g,b=255,0,0

for i in range(255*2):
    if i<255//3:
        g+=3
    elif i<255*2//3:
        r-=3
    elif i<255:
        b+=3
    elif i<255*4//3:
        g-=3
    elif i<255*5//3:
        r+=3
    else:
        b-=3
    t.fd(50+i)
    t.rt(91)
    t.pencolor(r,g,b)

t.done()