Create "pulsing" animated gifs with Pillow

animated_gif.py

from PIL import Image

colors = {
    'prearrival': (165, 226, 250, 255),
    'arrived': (253, 245, 210, 255),
    'waiting': (170, 255, 190, 255),
    'waiting_long': (255, 160, 159, 255),
    'unreviewed': (255, 160, 159, 255),
}

for name, color_values in colors.items():
    images = []

    for step in range(0,11):

        opacity = int(step * 0.1 * 255)
        img_number1 = str(step).zfill(2)
        img_number2 = 21 - step

        color = (color_values[0], color_values[1], color_values[2], opacity)

        base_image = Image.new('RGBA', (100,100), color='white')
        color_image = Image.new('RGBA', (100,100), color=color)
        new_image = Image.alpha_composite(base_image, color_image)
        images.append(new_image)

    all_images = images + images[::-1]
    images[0].save(f'output/{name}.gif', save_all=True, append_images=all_images, duration=10, loop=0)