Alpha colors

[waszqba]

Hi, I've noticed a tiny bug with android version of FAB.
When you set the background-color to rgba value with non-zero and non-one alpha value, the background actually shrinks, leaving the shadow intact, making the fab look like a button in a button.
Steps to reproduce:

1. create a sample app with FAB in the main view
2. give it a class like fab-transparent
3. create sass .fab-transparent class
4. create background-color: rgba(255, 255, 255, 0.4) in the .fab-transparent class (as it was in my case)
5. ???
6. profit