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Many d'Uccle chicks do not get their true colors until they are practically adults, so I wouldn't try to lable them just yet if they're young. 
In fact, even if these are older birds, then wait until they've molted at least once. The reason heavily white birds are non SQ as juveniles is because after a molt or 2 they'll be totally white. So I wouldn't assume the blue is not there at all. Like the white spots on my millie roos tail, it may take until the first molt for true colors to show up. 
If you're experimenting with color crosses then you have to be patient. What you see now is subject to change. Also, sunlight can affect the colors as well. My millie hens had much deeper brown feathers after their molt, but free-ranging has them looking much paler already.
Feathersite has photos of mostly SQ d'Uccles. What you describe sounds almost like a mottled red instead of blue or black...