>>17068948The first book wasn't interesting enough to make me bother reading the rest, but having a huge family of wizardborn gingers implies that wizards from imperial posessions were accepted. It's reasonable to suppose that an 1880s wizarding school would recognize Queen Victoria's subjects everywhere.
You could certainly come up with a canon-compatible explanation for a British-Isles-only acceptance policy, but by the 1880s that wouldn't be whites-only.
You could also come up with a canon-compatible whites-only acceptance policy, but it would be pretty unrealistic to accept gingers in that case.