Hi Guys,
TLDR;
Simple question: I got informed that ideasman claimed it would be possible to render vertex colors (REAL vertex colors, not the ones only available per face) in the viewport by overriding a draw callback. I would love to know how to do that.
Ideally, someone could post a minimum working example, but actually I take the tiniest hint I can get! 
Thank you!
Background (unnecessary additional info):
Recently Gottfried Hofmann informed me that he talked to ideasman via IRC the other day and he mentioned that it would be possible to add an own custom-data layer to vertices and then call my own drawing callback. Ideally vertex buffers would be used instead of glVertex, ofc.
I am looking for around 4 years to do that and although I already wanted to give up multiple times, this gave me a little hope. Last year, I mentioned in my BCon17 talk (https://www.youtube.com/watch?v=PMYET5LA-Kg), that I desperately miss this feature - unfortunately my original BlenderArtists posting was not converted to the new version. But today I saw this thread on here: Gradient vertex color for proportional editing which already shows how nice this will look, but is this even accessable yet for us? I know the Python API is subject to change, but maybe someone is kind and can shed some light on this topic. I would really buy a beer for someone who can provide a minimum working example (just send me your PayPal address and I will transfer 2 Euros 
honestly… )
As I already said above - every tiny little help in this regard is greatly appreciated! Thank you!
Kind regards,
BlenderEi (Adam)