This is using @MaximBelov's fork, version 0.5.4.
Custom backgroundColor on a pie chart's datasets are ignored, see https://jsfiddle.net/8erzf0hn/

It works (i.e. chart shows the expected custom colors) if you
- switch to 2.9.4/0.4.0 (legacy code, image on the left);
- do not import the colorschemes plugin
- set the colors as a custom scheme (uncomment the options)