AlphaPicker with vertical direction is upside down
The vertical alpha picker has the 100% alpha point at the bottom, an 0% at the top, which is not a common convention, I needed to change this, I dont see a way to do it in the docs, Kindly update me on this, if its been added, or if there is a workaround to get this fixed, 

<img width="72" alt="picker" src="https://user-images.githubusercontent.com/33175290/81388798-724afd00-9136-11ea-834a-dc0dbe0501b1.png">
