Chirper and Randy have given you some great resources! If you want to see some pictures of Mallorn, I can post some on here for you!
I would like to add that as babies, yellowface II budgies look like yellowface I. The blue and yellow usually don't combine to form that lovely seafoam color until after the first moult
And about horse genetics: I find that horse genetics are much easier than bird genetics because with birds, there are hundreds of combinations and mutations that can overlap or cover others.
I've been into bird genetics for many years and I still have my confusing moments
Good luck with finding more info!