incorrect Colorbar for log values in scatter plot

问题

I want to use a scatter plot to describe the relationship between X, Y and Z. Z is p-value so it is better to denote it as log values.

Following the instructions here, I can plot a logarithmic scatter plot, but the color bar seems wrong. The color bar is almost totally blue, but there should be some red! Below is the figure and my codes.

import matplotlib
import matplotlib.pyplot as plt
import seaborn as sns
from matplotlib.colors import LogNorm

fig = plt.figure()
ax1 = fig.add_subplot(1,1,1)
ax1.set_title("P-value")

Z1 = pos_spearmanr['pval']
X = pos_spearmanr['X']
Y = pos_spearmanr['Y']

im = ax1.scatter(X,
                 Y, 
                edgecolors=None,
                c=Z1,
                norm=LogNorm(),
                cmap=plt.get_cmap('bwr'), alpha=0.2)

ax1.set_xlabel('X')
ax1.set_ylabel('Y')
ax1.set_xlim(0, 1)
ax1.set_ylim(0, 1)
cbar = fig.colorbar(im,ax=ax1)

来源：https://stackoverflow.com/questions/35004088/incorrect-colorbar-for-log-values-in-scatter-plot