Pink and Blue artefacts appearing in the notification centre
I do have exactly the same artefacts on MacBook 2016 1.2 Ghz.
They appearing when there's some window under the notification centre. Can be seen on FaceTime app window sometime as well.

Looks like a software/driver issue so far.

Update: 
Tried it with clean install of El Capitan — it's not there, everything is ok. So it is a Sierra bug. Reported it to Apple via Bug Reporter as a 10.12 bug.