I honestly don't know...but I do know that my Max is very dark (well, he's almost the same as he was when he was a puppy...like they all are...only he's gotten some silver..or 'blue") and I can't see that he's lightened up much at all to speak of. He's almost 3 (next month) and his sister is a lot lighter than he is, but still not blonde like I've seen a lot of other babies here are.
I just know that when we first got Max and just thought he was so cute, and we hoped he'd stay exactly the colors he was (and we got our wish pretty much), but I have to say that if he'd turned yellow and green, we would have loved him just the same (obviously, we're not interested in breeding, LOL). I am interested in other answers though, so I'm so glad you posted this! And we're keeping Bleu in our prayers, the little angel boy
.