Upgrading from 14.04 to 16.04 produces a display with way too much black

[AlainKnaff]

1.) alain@alain-pc:~$ lsb_release -rd
Description: Ubuntu 16.04.2 LTS
Release: 16.04

2.) alain@alain-pc:~$ apt-cache policy xserver-xorg-video-nouveau
xserver-xorg-video-nouveau:
  Installed: 1:1.0.12-1build2
  Candidate: 1:1.0.12-1build2
  Version table:
 *** 1:1.0.12-1build2 500
        500 http://be.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status

3.) What you expected to happen
A nice and colorful display of my KDE desktop, where I can actually recognize the features (panel, command entry widget, etc.) rather than have to grasp for them in the dark.

4.) What happened instead
After a do-release-upgrade going from 14.04 to 16.04
Entire desktop is composed of black or very dark grey items, which can almost not be seen (but present, as the elements do react when clicked upon)

After uninstalling xserver-xorg-video-nouveau (and all packages that depend on it), dpkg --purge, and then re-installing it, everything was nice and colorful.

Took a non-trivial amount of googling to find this solution though (... after many non-solutions)