python的matplotlib 3D怎么更换背景颜色？

Question

from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt
import numpy as np
plt.rcParams['font.sans-serif']=['STSong']
plt.rcParams['axes.unicode_minus']=False
fig=plt.figure()
ax=fig.add_subplot(111,projection='3d')
a=np.arange(0,1,0.1)
b=a*2
c=2*np.sin(a)
ax.scatter(a,b,c,color='green')
ax.set_xticks([])
ax.set_yticks([])
ax.set_zticks([])
ax.set_xlabel("甲")
ax.set_ylabel("乙")
ax.set_zlabel("丙")
ax.grid(False)
plt.show()

如何把银灰色去掉啊？