I use [matplotlib.pyplot.pcolor()](http://matplotlib.org/api/pyplot_api.html?highlight=pcolor#matplotlib.pyplot.pcolor) to plot a heatmap with matplotlib:

```
import numpy as np
import matplotlib.pyplot as plt    

np.random.seed(1)
data =  np.sort(np.random.rand(8,12))
plt.figure()
c = plt.pcolor(data, edgecolors='k', linewidths=4, cmap='RdBu', vmin=0.0, vmax=1.0)
plt.colorbar(c)
plt.show()

```

[![enter image description here](https://i.stack.imgur.com/n34iL.png)](https://i.stack.imgur.com/n34iL.png)

How can I change the intensity of the `'RdBu'` colormap? E.g., if the color is `(0, 0, 1)`, it should be transformed into `(0, 0, 0.8)`. More generally, 
if the color is `(x, y, z)`, it should be transformed into `(ax, ay, az)`, where `a` is some scalar between zero and one.