Google colaboratoryでの画像保存について

前提・実現したいこと

google colaboratoryで、散布図の機能を利用して、ランダムに透明度の異なるグラフの画像を大量に作成したいと考えております。

発生している問題・エラーメッセージ

求めている画像（ランダムな透明度）は表示されるのですが、保存された画像を見ると全て同じ透明度の画像になっています。

該当のソースコード

for cnt in range( 10 ):

import random

import matplotlib.pyplot as plt
from matplotlib import patches
from google.colab import files

fig, ax = plt.subplots(figsize=(6,6))

ax.set_xlim(0, 6)
ax.set_ylim(0, 6)
ax.set_xticks([])
ax.set_yticks([])

c15 = patches.Circle( (1,5), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c25 = patches.Circle( (2,5), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c35 = patches.Circle( (3,5), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c45 = patches.Circle( (4,5), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c55 = patches.Circle( (5,5), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c14 = patches.Circle( (1,4), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c24 = patches.Circle( (2,4), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c34 = patches.Circle( (3,4), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c44 = patches.Circle( (4,4), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c54 = patches.Circle( (5,4), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c13 = patches.Circle( (1,3), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c23 = patches.Circle( (2,3), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c33 = patches.Circle( (3,3), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c43 = patches.Circle( (4,3), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c53 = patches.Circle( (5,3), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c12 = patches.Circle( (1,2), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c22 = patches.Circle( (2,2), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c32 = patches.Circle( (3,2), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c42 = patches.Circle( (4,2), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c52 = patches.Circle( (5,2), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c11 = patches.Circle( (1,1), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c21 = patches.Circle( (2,1), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c31 = patches.Circle( (3,1), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))
c41 = patches.Circle( (4,1), 0.3, facecolor="red", alpha=random.uniform(0.11, 0.50))
c51 = patches.Circle( (5,1), 0.3, facecolor="red", alpha=random.uniform(0.96, 1.00))

ax.add_patch(c15)
ax.add_patch(c25)
ax.add_patch(c35)
ax.add_patch(c45)
ax.add_patch(c55)
ax.add_patch(c14)
ax.add_patch(c24)
ax.add_patch(c34)
ax.add_patch(c44)
ax.add_patch(c54)
ax.add_patch(c13)
ax.add_patch(c23)
ax.add_patch(c33)
ax.add_patch(c43)
ax.add_patch(c53)
ax.add_patch(c12)
ax.add_patch(c22)
ax.add_patch(c32)
ax.add_patch(c42)
ax.add_patch(c52)
ax.add_patch(c11)
ax.add_patch(c21)
ax.add_patch(c31)
ax.add_patch(c41)
ax.add_patch(c51)

plt.savefig('testim.png')
files.download('testim.png') 
plt.show()