I don't know what you mean by 'do it with update 2', but since a 21 and a 30 should produce something in the 23-28 range, and most likely a 25 or 26, getting a 15 or a 16 is very unlikely.

As I mentioned, having children with totally random hair colors is normal. It's not terribly common, but it happens, and there's no known connection between them; they're apparently random. This is likely the reason a 15 was produced from 30 and 21.

EDIT: Or perhaps you think I meant to respond to update two? No, I intended to respond to the post I quoted. Your result was outside the expected range - even you commented on it. As I posted, this is possibly because it was a random head type that randomly fell close to, but not within, the expected range.