So we're back at the point we were before - is there something special about the relationship between Hagos and Biasutti that allows this transfer of expertise just by citation? My point is that it takes years of training, experience and recognition by others in the field to be considered an expert in that field. You seem to be saying Hagos got it just by citing Biasutti. If David Attenborough cited Niels Bohr would he become an expert in Physics? No he wouldn't, he'd just be an expert in biology who happened to cite an expert in physics once - we wouldn't be able to accept anything he said about quantum mechanics or block holes as fact until we checked it with a genuine expert in the field. So what makes you think Hagos has become an expert in human skin colour just by citing Biasutti? And remember that the policy doesn't just state "expert",  it states "established expert in the topic whose previous work in the field has been published by reliable third-party publications" - unless you are you going to argue that Hagos got Biasutti's reputation and previous publications as well I think this is a dead end argument. You should accept that Hagos doesn't meet the criteria laid down by the WP policy for the creators of self-published sources.
If you don't think that Hagos chose the colours for each country then who do you think did it? They didn't just magically change due to "migration trends" - somebody made a decision that colour X goes in country Y. From the evidence we have it would appear that Hagos was the one who made that decision - it certainly wasn't made by Biasutti or the writers of the national census data that he cites as his sources.
It makes no difference to the situation so I won't argue it, but for the record I don't accept that Hagos is a recognised expert on migration.