I could be very wrong, so take my reply with a grain of salt and wait for someone with much more experience than I have. I have only just started in lavenders myself, but unlike you I have no lavender roosters. I am using black roosters on lavender hens. The sex flip may alter the color outcome, but Im not sure. We'll both be learning from your question I hope!
Anyways.. in my case, I was told that if I use my black rooster over my lavender hens, the chicks will all be black but would carry the lavender gene. Meaning I can cross those chicks to themselves (or other carriers) and get about a quarter which are lavender color, several non lavender but lavender carriers, and the rest blacks with no lavender gene.
This is, however, what I was told on a LangshanX color program. Not a d'anver program. I havent hatched my F1's from the above scenario yet, still about a week to go, so as of now I'm just waiting to see what comes.