There is no such thing as a 'locale' - not 'local' amelanistic alterna cross. As for the number of generations before it would be pure - you can't get there from here. It could be seven million years of evolution from this point forward - would never make it a pure alterna albino. You would have better luck focusing on producing as many alterna as possible with the hopes that you randomly produce an albino rather than raise up each successive generation to breed back to an alterna to get less and less ruthveni blood. There is nothing wrong with appreciating an alterna hybrid for what it is rather than trying to masquerade it as pure.