pulse.py

from gpiozero import TrafficLights

lights = TrafficLights(4, 5, 6, pwm=True)

def pulse():
    while True:
        for i in range(10):
            lights.green.value = i / 10
            sleep(0.01)
        for i in reversed(range(10)):
            lights.green.value = i / 10
            sleep(0.01)
            
lights.red.source = lights.green.values
lights.amber.source = lights.green.values

pulse()