Hmmm, ok, I'm less convinced that it is so bad. If this is known (and desirable functionality) I suggest that you set the data values to zero *after* imsave so that we are testing the clearing of RGB values. So something like:

```
bad_alphas = alphas < 1./255
...
plt.imsave(buff, data)
...
data[bad_alphas] = 0
```