Muscovy egg getting a blue spot?

[CasualT]

I've been incubating Muscovy eggs and am down to just 2 days till lockdown. I candled today and think only 1 is left alive. However, the one that's alive has suddenly got a big blue dark spot on it. Has this happened to anyone else? I know he's alive, I saw his bill popping up in the air cell. Does that mean he is internally pipped? Anyway, just wondering if this is normal.