This is not an obvious case actually, and I can point out a few things for you here.
In terms of your Labidochromis Caeruleus, often I have fry that come out VERY pale, almost white and it's just a matter of time before the color sets in. The barred ones, this is actually the norm, not a sign of hybridization. Well it COULD be, but I seriously doubt that on that basis.
What's commonly seen in this species in wild caught ones show bars many times. The pure solid yellow look is something aquarists strive for, but if you examine many wild caught ones, they do show quite a few bars.
Again on the coloring, if you examine wild caughts or wild inhabited ones, this species was first discovered as blue and if I am correct, Caeruleus is greek for blue or blue fish, something like that. They have also found this species has a totally white varient as well.
If you have males of the Labs in there, I don't think they crossed with your supsect Johanni. Wait until the fry grow out a bit more and post some shots please.