Excellent answer but I will add that phenotyping eye color also adds noise - 23andMe relies on questionnaires and the users have some discretion in identifying

Excellent answer but I will add that phenotyping eye color also adds noise - 23andMe relies on questionnaires and the users have some discretion in identifying their own eye color for example. And since the trait seems so polygenic you do need a ton of samples. The computation complexity isn't as big a deal because the data here is genotyped not sequenced.