White tips is quite normal on juvenile plumage of black and solid lavender birds. That does not indicate the mottling gene. The mottled chicks from this project do not hatch out black or lavender, but a creamy/yellow color. They also do not have dark legs, but white legs, which is a way to identify them in your adults. Since the mottling doesn't really come in until the 2nd year, it is hard to tell otherwise unless you hatched them yourself.