What I can tell you is the few that stayed that smokey color were all boys (sex link maybe or just coincidence?) and they look like a combination of black and lavender together which gives them this silvery black look. They are definitely carrying lavender because mated with a lavender hen they...
Check out my post on the previous page it may be the same thing I have in my lavender flock as well :)
I would definitely tag that chick because my guess is it will turn completely black and will get lost in your black splits.
There could be something possibly to the mutation theory as I had it in my flock of lavenders as well. I was breeding from blacks (definite blacks no blues) that were split to lavender and I was hatching lavenders, blacks and the occasional grey/ blue chick. I was very confused at the time...